THE  ELECTRIC  FURNACE 


ITS  EVOLUTION,  THEORY  AND 
PRACTICE 


BY 


ALFRED    STANSFIELD,    D.Sc, 
1 1 

ASSOCIATE  OF  THE  ROYAL  SCHOOL  OF  MINES 

PROFESSOR  OF  METALLURGY  IN  McGiLL  UNIVERSITY 

MONTREAL 


WITH    FIFTY-THREE    ILLUSTRATIONS 


THE    CANADIAN    ENGINEER 

TORONTO 


HILL    PUBLISHING   COMPANY 

NEW    YORK    AND    LONDON 


GENERAL 


Entered  according  to  Act  of  the  Parliament  of  Canada,  in  the  year  one 
thousand  nine  hundred  and  eight,  by  ALFRED  STANSFIELD,  D.Sc., 
at  the  Department  of  Agriculture. 


PREFACE. 


On  my  first  visit  to  Canada,  in  1897,  I  constructed  an  electric 
furnace  and  showed  it  in  operation  at  a  lecture  on  Canada's 
metals,  which  was  delivered  by  the  late  Sir  William  Roberts- 
Austen.  The  application  of  electrical  heat  to  Metallurgy  has 
always  interested  me  greatly  and  I  hope  that  this  little  book 
may  serve  to  instil  this  interest  in  others,  and  to  help  forward 
the  application  of  electric  smelting  in  a  country  which  is  so  rich 
in  water-powers  and  mineral  resources. 

This  book  originated  in  a  series  of  papers,  written  about 
a  year  ago  for  the  "Canadian  Engineer,"  in  which  I  endeavoured 
to  present,  as  simply  as  possible,  the  principles  on  which  the 
construction  and  use  of  the  electric  furnace  depend,  and  to  give 
an  account  of  its  history  and  present  development. 

The  original  papers  were  written  at  a  time  when  the  experi- 
ments of  Dr.  Haanel,  at  Sault  Ste.  Marie,  wrere  attracting  public 
attention,  and  a  large  section  of  the  book  has  been  devoted  to 
the  consideration  of  these  and  other  advances  in  the  electro- 
metallurgy of  iron  and  steel. 

I  wish  to  thank  all  who  have  helped  me  in  the  preparation 
of  this  book,  including  Dr.  Haanel,  whose  valuable  monographs 
have  formed  the  basis  of  my  chapter  on  iron  and  steel,  and  to 
whom  I  am  indebted  for  additional  information  on  this  branch 
ot  the  subject :  Prof.  J.  W.  Richards,  who  has  taken  an  interest 
in  my  work,  and  whose  book  on  "Metallurgical  Calculations" 
has  been  of  considerable  assistance  in  writing  the  chapter  on 
furnace  efficiencies ;  Mr.  E.  A.  Colby,  who  gave  me  information 
in  regard  to  his  induction  steel  furnace  and  a  sketch  for  Fig.  25  ; 
Mr.  Francis  A.  J.  Fitzgerald,  who  supplied  me  with  the  data 
for  Table  X.;  the  editor  of  the  "Electrochemical  and  Metal- 
lurgical Industry,"  who  loaned  the  block  for  the  frontispiece, 
and  the  International  Acheson  Graphite  Company,  who  gave 
me  information  about  their  furnaces  and  lent  the  block  for 
Fig.  40.  I  also  wish  to  thank  those  of  my  personal  friends  who 
assisted  me  in  the  tedious  work  of  proof-reading. 

ALFRED  STANSFIELD. 
November,   1907. 
Mr(iill    University,   Montreal, 


174579 


CONTENTS. 


CHAPTER  I. 

History  of  the  Electric  Furnace. 

Page. 

The    electric    arc        i 

W.    Siemens'   electric  furnaces        3 

Cowles  brothers'  electric  furnaces       5 

Hall  and  Heroult  aluminium  processes        6 

H.   Moissan's  researches        7 

Production   of  the  diamond         Q 

Willson's  carbide  furnace 1) 

Carborundum       10 

Ferro-alloys 12 

Iron  and  steel       12 

CHAPTER  II. 
Description  and  Classification  of  Electric  Furnaces. 

Definition  of  electric  furnace       15 

Heat  produced  by  electric  current        16 

Essential  parts  of  electric  furnace 17 

Classification  of  electric  furnaces 18 

Arc  furnaces 19 

Resistance  furnaces       21 

with    special  resistor         . ...  21 

without   special  resistor        26 

electrolytic         30 

CHAPTER  III. 

Efficiency  of  Electric  and  other   Furnaces,  and   Relative   Cost  of 
Electrical  and  Fuel  Heat. 

Page. 

Cost  of  electrical  energy       33 

Efficiency  of  furnaces      34 

Calculation  of  furnace  efficiencies       37 

Heat   units          38 

Melting  temperatures  of  metals,  and  amounts  of  heat  required  to 

melt  them        40 

Calorific  power  of  fuel       41 

Table  of  calorific  powers 43 

Calculation  of  efficiency  of  electric  steel  furnace      45 


vi.  CONTENTS. 

CHAPTER  IV. 
Electric  Furnace  Design,  Construction  and  Operation. 

General  considerations        48 

Materials  of  furnace  construction       49 

Fireclay  bricks        40 

Silica  bricks         50 

Lime          50 

Magnesia         51 

Dolomite          52 

Alumina        52 

Carbon        53 

Carborundum        54 

Siloxicon          54 

Table  of  refractory  materials        55 

Heat  insulation       56 

Table  of  heat  conductivities        57 

Furnace  walls  without  refractory  materials 58 

Production  of  heat  in  electric  furnaces      60 

Voltage  required  for  electric  furnaces 66 

Voltage  of  arc  furnaces         67 

Voltage  of  resistance  furnaces       69 

Regulation  of  electric  smelting      71 

Resistors        73 

Electrical    resistivity          75 

Resistivity  of  powdered  coke          75 

Resistivity  of  carbon  rods       76 

Resistivity  of  molten   slags  and  iron        78 

Electrodes 79 

Electrode  holders        80 

Measurement  of  furnace  temperatures        82 

Conclusion         83 

CHAPTER  V. 
Production  of  Iron  and  Steel   in  the   Electric  Furnace. 

Varieties  of  Iron  and  Steel       ....    85 

I.  Production  of  steel  from  scrap,  pig-iron  and  iron  ore 86 

Heroult   steel   furnace          86 

Keller    steel    furnace         92 

Kjellin    steel    furnace            93 

Colby  steel  furnace       96 

Gronwall  steel  furnace        101 

Gin  steel  furnace      105 

Girod  steel  furnace       106 

II.  Production  of  pig-iron  from  iron  ore,  carbon  and  fluxes....  107 

Heroult  ore-smelting  furnace       108 

Keller  ore-smelting  furnace       1 1 1 

Harmet  ore-smelting   furnace         113 

Haanel-Heroult  furnace       115 

Turnbull-Heroult  furnace       117 

Plants  for  the  electric  smelting  of  iron  ores   120 

Possibilities  in  the  electric  smelting  or  iron  ores 121 

III.  Direct  production  of  steel  from  iron  ore       129 

Stassano  steel  furnace        129 

Elimination  of  sulphur  and  phosphorus        132 

Conclusion       135 


CONTEISTS.  vii. 

CHAPTER  VI. 
Other  Uses  of  the  Electric  Furnace. 

I.  The  ferro-alloys         136 

Analyses  of  ferro-alloys        139 

I 1.  Graphite  and  the  carbides      142 

Graphite         142 

Kryptol         149 

Carborundum        149 

Siloxicon        1 53 

Calcium  carbide        1 54 

III.  Electrothermic  production  of  zinc       155 

Cowles  zinc  furnace       1 57 

Johnson  zinc  furnace       1 57 

Laval  zinc  furnace         1 59 

Salgues  zinc  furnace       160 

Conditions  for  obtaining  liquid  zinc       162 

Experimental  zinc  furnace       164 

Snyder    zinc   process          165 

Snyder  zinc  furnaces 167 

Electrical  energy  required  for  zinc  smelting 170 

IV.  Miscellaneous  uses  of  the  electric  furnace     171 

Silicon 171 

Fused  quartz        172 

Glass       172 

Alundum          173 

Nitric  acid        173 

Phosphorus          174 

Carbon    bisulphide 174 

V.  Electrolytic  processes 174 

Electrolysis       1 74 

Acker  caustic  soda  process 177 

Castner  sodium  process         179 

Ashcroft   sodium  process         181 

Swinburne  and  Ashcroft  chlorine-smelting  process      ....  184 

Aluminium        185 


CHAPTER  VII. 
Future  Developments  of  the  Electric  Furnace. 

General  considerations       ......................................  189 

Exhaustion  of  coal  supplies        .................................  190 

Utilization  of  water-powers        ..................................  191 

Achievements  of  the  electric  furnace       .........................  191 

Probable  uses  of  the  electric  furnace  in  the  future  .............  192 

Other  sources  of  electric  power        .............................  194 


index 


viii.  LIST  OF  ILLUSTRATIONS. 

LIST  OF  ILLUSTRATIONS. 


Frontispiece:  Colby  Induction  Steel  Furnace. 

Fig.  Page. 

1 .  Electric    arc         i 

2.  Siemens'  vertical  arc  furnace       4 

3.  Siemens'  horizontal  arc  furnace       5 

4.  Cowles  furnace  for  aluminium  alloys       £ 

5.  Aluminium   furnace        7 

6.  Moissan  furnace        8 

7.  Willson  carbide  furnace 10 

8.  Acheson   carborundum   furnace        •  •  1 1 

g.  Electric    circuit         15 

10.  Independent  arc  furnace       19 

1 1.  Direct-heating  arc  furnace       20 

12.  Electrical    tube  furnace         21 

13.  Electric  crucible  furnace 22 

14.  Borchers'   resistance   furnace        24 

1 5.  Tone  resistance  furnace        25 

1 6.  Shaft  furnace  with  lateral  electrodes       27 

17.  Shaft  furnace  with  central  electrodes       28 

1 8.  De  Laval  ore-smelting  furnace       29 

19.  Electrolytic  furnace        30 

20.  Losses  of  heat  in  melting  metals       35 

21.  Ideal  electric  furnace       48 

22.  Electrode  Holder  of  Heroult  Steel  Furnace     81 

23.  Heroult    steel  furnace 87 

24.  Kjellin  Steel  furnace        93 

25.  Colby    induction   furnace           ;  .  .  .  .  97 

26  8-ton  induction  steel  furnace        100 

27.  Induction  furnace  with  shielded  core       103 

28.  Gin  steel  furnace 104 

29.  Heroult  ore-smelting  furnace        108 

30.  Keller  furnace       112 

31.  Harmet  furnace 114 

32.  Haanel-Heroult   furnace         1 16 

33.  Turnbull-Heroult   furnace         1 18 

34.  and  35.   Connections  for  electric  furnace      119 

36.  Ideal   furnace   (for   smelting  iron   ores)      122 

37.  Stassano  furnace 130 

38.  Acheson  graphite  furnace       145 

39.  Acheson  electrode  furnace         145 

40.  Carborundum   furnace  burning        151 

41.  Multiple   core    furnace         154 

42.  Cowles   electric   zinc   furnace         157 

43.  Johnson  electric  zinc  furnace      158 

44.  Laval  electric  zinc  furnace        1 59 

45.  Salgues  electric  zinc  furnace       160 

46.  Experimental  zinc  furnace       163 

47.  Snyder   induction   furnace        166 

48.  Snyder  furnace  for  obtaining  liquid  zinc      168 

49.  Acker  caustic  soda  furnace       178 

50.  Castner  sodium  furnace       180 

51.  Ashcroft   sodium  furnace        182 

52.  Aluminium  furnace         186 


LIST   OF   TABLES.  ix. 


LIST    OF    TABLES. 

Table.  Page. 

I.  Classification  of  electric  furnaces        32 

II.  Net  efficiencies  of  furnaces  used  for  melting  metals     ....  34 

III.  Melting    temperatures   of    metals,    and    amounts    of   heat 

required  to  melt  them        40 

IV.  Calorific  powers        43 

V.  Refractory  materials        55 

VI.  Heat  conductivities  of  furnace  materials 57 

.' 

VII.  Voltage  of  Moissan's  arc  furnace       68 

VIII.  Resistivity  of  graphitized  coke  powder      76 

IX.  Resistivity  of  solid  carbon       77 

X.  Resistivity  of  amorphous  and  graphitic  carbon       78 

XI.  Operation  of  5-ton   Heroult  furnace        89 

XII.  Induction  furnaces  in  operation  or  in  course  of  construc- 

tion            99 

XIII.  Steel  and  slag  analyses      134 

XIV.  Analyses  of  ferro-alloys        139  &  140 


INTRODUCTION. 


The  rapid  growth  of  the  electric  furnace  makes  it  increas- 
ingly difficult  for  the  metallurgist  to  keep  in  touch  with  its 
recent  developments.  A  few  years  ago  it  was  a  scientific 
curiosity  ;  now  it  threatens  to  rival  the  Bessemer  converter,  the 
open-hearth  steel  furnace,  and  even  the  blast  furnace  itself. 

The  halo  of  romance,  that  has  always  surrounded  electricity 
in  all  its  forms,  has  caused  the  wildest  schemes  to  be  originated, 
and  has  given  them  a  hearing ;  while,  on  the  other  hand,  prac- 
ticable electric  smelting  processes  have  been  considered  visionary. 

In  this  book,  it  has  been  the  author's  purpose  to  trace  the 
evolution  of  the  electric  furnace  from  its  simplest  beginnings, 
and  to  set  forth,  as  briefly  as  is  consistent  with  clearness,  the 
more  important  facts  relating  to  its  theory  and  practice. 

No  attempt  has  been  made  to  give  a  description  of  all  the 
electric  furnaces  that  have  been  invented,  but  rather  to  set  forth 
clearly  the  fundamental  principles  of  this  form  of  furnace ;  to 
show  its  various  uses ;  to  indicate  its  limitations ;  and,  if  pos- 
sible, to  be  of  some  assistance  to  those  who  wish  to  design 
electric  furnaces,  or  to.  judge  of  the  feasibility  of  schemes 
involving  their  use. 

The  scope  of  the  book  can  be  gathered  from  the  titles  of 
the  seven  chapters  of  which  it  is  composed.  The  first  is  his- 
torical, the  next  three  relate  to  the  classification,  efficiency  and 
design  of  electric  furnaces,  while  Chapters  V.  and  VI.  are 
devoted  to  the  manufacture  of  iron  and  steel,  and  other  products 
of  the  electric  furnace.  Chapter  VII.  is  an  attempt  to  look  into 
the  future  and  to  note  the  directions  in  which  electrical  heating 
may  be  expected  to  develop. 


FRONTISPIECE 


COLBY   ELECTRIC   STEEL   FURNACE 


From  ELECTROCHEMICAL  INDUSTRY. 


THE    ELECTRIC   FURNACE. 


Its  Evolution,  Theory  and  Practice. 


CHAPTER  I. 
History  of  the  Electric  Furnace. 

The  electric  furnace  is  of  comparatively  recent  origin.  The 
first  of  any  practical  importance,  was  constructed  by  Sir  W. 
Siemens  in  1878*,  and  in  i882t  he  melted  in  an  electric  furnace 


Fig.    i. — The  Electric  Arc. 

some  twenty  pounds  of  steel  and  eight  pounds  of  platinum.     Since 
that  time  the  development  has  been  rapid. 

The  beginning  of  the  electric  furnace  may,  however,  be 
traced  much  farther  back  than  this.  In  1800 — only  a  few  months 
after  Volta's  discovery  of  the  electric  battery — Sir  Humphry 
Davy,  experimenting  with  the  new  battery,  produced  the  first  arc 
light  between  carbon  points, t  and,  as  the  electric  arc  is  the  source 
of  heat  in  an  important  class  of  electric  furnaces,  its  discovery 
was  the  first  step  in  their  evolution. 

*Siemens'   Electric   Furnace,   Journ.   Soc.   of  Telegraph   Engineers,  June,   1880. 
•f-Siemens  and  Huntingdon,  British  Assoc.  for  the  Adv.  of  Science,  1882,  p.  496. 
JDavy,  S.    P.   Thompson's  Electricity   and   Magnetism,  Phil   Trans.   Roy     Soc.,   vol 
xcvii.    (1809),   p.    71,   and  vol.    cxi.    (1821),   p.    427. 


2  THE     ELECTRIC     FURNACE. 

The  electric  arc,  as  shown  in  Fig.  i,  may  be  produced  by 
passing  an  electric  current  through  two  carbon  rods  which  touch 
each  other  and  then  drawing  them  apart.  The  arc  consists  of  a 
flame  of  vaporized  carbon,  extending  from  one  carbon  pole  to  the 
other.  When  an  electric  current  meets  with  resistance,  it  is  trans- 
formed into  heat,  and,  as  the  carbonaceous  vapour  offers  a  con- 
siderable resistance  to  the  electric  current,  a  very  high  temperature 
is  produced  ;  high  enough  to  melt  or  vaporize  any  known  substance. 

In  the  direct  current  arc  the  positive  carbon,  which  is  marked 
+  in  the  figure,  is  hollowed  out  by  the  current,  and  becomes  in- 
tensely white  hot,  presenting  the  dazzling  bright  light  with  which 
all  are  acquainted.  The  arc  light  is,  in  fact,  a  miniature  electric 
furnace  of  the  arc  type ;  and  produces  a  temperature  not  much  in- 
ferior to  that  in  any  modern  electric  furnace.  It  has  been  sup- 
posed that  the  hollowing  out  of  the  positive  carbon  is  due  to  an 
electrolytic  conveyance  of  carbon  from  the  positive  to  the  negative 
electrode ;  but  recent  experiments  show  that  any  electrical  transfer 
of  carbon  is  in  the  other  direction,  being  a  stream  of  electrons 
from  the  negative  electrode,  like  the  kathode  discharge  in  a 
vacuum  tube.  The  bombardment  of  the  positive  carbon  by  this 
stream  of  electrons,  generates  so  much  heat  that  the  electrode  be- 
comes white  hot  and  rapidly  evaporates,  thus  producing  the  char- 
acteristic crater-like  form. 

This  explanation  appears  to  fit  in  well  with  the  appearance  of 
an  arc  that  has  been  drawn  out  to  a  little  more  than  its  normal 
length.  The  arc  (which  should  only  be  observed  through  a  dark- 
colored  glass  screen)  will  be  noticed  to  stream  freely  from  the  tip 
of  the  negative  electrode,  and  its  starting-point  on  this  electrode 
is  unaffected  by  drafts  or  magnetic  influences.  The  current  passes 
with  difficulty  on  to  the  positive  electrode,  and  does  not  always 
select  the  point  nearest  to  the  negative  electrode,  but  is  blown 
about  and  wanders  over  a  considerable  area  of  the  electrode.  The 
temperature  of  the  hottest  part  of  the  positive  carbon  in  the 
electric  arc  has  been  measured,  and  is  considered  to  be  about 
3,7oo°C.  (6,7oo°F.),  which  is  twice  the  temperature  of  melting 
platinum  or  melting  quartz,  and  more  than  twice  the  temperature 
of  the  open-hearth  steel  furnace. 

In  the  use  of  a  direct  current  arc  for  lighting,  it  is  usual  to 
make  the  upper  carbon  the  positive  electrode,  in  order  to  throw 
the  greatest  illumination  downwards.  In  Fig.  i  this  arrangement 
has  been  reversed,  and  in  this  position  the  positive  carbon  serves 


HISTORY.  3 

as  a  miniature  cup  in  which  any  substance  can  be  placed  in  order  to 
study  its  behavior  at  these  high  temperatures. 

The  writer  has  placed  a  small  cylinder  of  refractory  material 
around  the  lower  carbon  of  such  an  arc,  and,  with  this  simple 
apparatus,  was  able  to  repeat  some  of  Moissan's  well-known  ex- 
periments on  the  production  of  the  diamond. 

In  another  form  of  electric  furnace,  the  heat  is  produced  by 
the  passage  of  the  electric  current  through  a  solid  or  liquid  con- 
ductor. This  method  of  producing  electrical  heat  is  typified  in 
the  common  incandescent  lamp.  The  earliest  use  of  this  method 
cf  heating  was  in  1815,  when  W.  H.  Pepys*  solved  an  important 
question  in  regard  to  the  nature  of  steel  by  means  of  a  miniature 
resistance  furnace  operated  by  a  battery.  .  He  placed  some 
diamond  dust  (a  pure  form  of  carbon)  in  a  cut  in  a  piece  of 
wrought  iron  wire,  and  passed  an  electric  current  through  the 
wire,  thus  heating  it  to  redness.  The  iron  absorbed  the  diamond 
dust  and  became  converted  into  steel. 

Although  the  principle  of  electric  heating  had  thus  been  dis- 
covered early  in  the  century,  very  little  progress  was  made  with 
the  practical  application  of  this  source  of  heat  until  the  discovery 
of  the  dynamo.  Among  those  who  attempted  to  utilize  electrical 
heat  in  small  furnaces,  with  the  aid  only  of  powerful  electric  bat- 
teries, may  be  mentioned — Napier,  who,  in  1845,  produced  a  small 
arc  in  a  plumbago  crucible,  intending  to  reduce  certain  metals 
from  their  ores;  Despretzt,  who,  in  1849,  made  a  small  tube  of 
charcoal,  about  an  inch  long,  and  heated  it  by  passing  through 
it  an  electric  current  from  a  battery  of  600  Bunsen. cells ;  and 
Pichou,t  who  described,  in  1853,  a  furnace,  heated  by  a  series 
of  electric  arcs.  The  furnace,  which  was  probably  never  con- 
structed, was  intended  for  the  reduction  of  metallic  ores.  Joule 
and  Thompson  also  attempted  to  utilize  the  high  temperature  of 
the  electric  arc. 

Until  the  invention  of  the  dynamo,  in  1867,  experiments  re- 
quiring any  considerable  amount  of  electrical  power  could  only 
be  conducted  at  great  trouble  and  expense  by  means  of  electric 
batteries.  Sir  W.  Siemens,  with  the  aid  of  the  dynamo,  began, 
in  1878,  to  experiment  on  the  electric  furnace,  which  he  used 
mainly  for  melting  metals.  The  form  of  furnace  usually  associated 


*Phil.   Trans.   Roy.    Soc.,   1815,  vol.   cv.,   p.    371. 

fDespretz,   Comptes   Rendus   de    1'Acad,   des  Sciences,   vol.   xxviii.,   p.    755,   and   vol. 

xxix.,    pp.    48,    545,    712,    (1849). 
^Mentioned   by   Andreoli,   Industries,   1893,   see  Borchers'   Electric   Smelting. 


THE     ELECTRIC     FURNACE. 


with  his  name*  is  shown  in  Fig.  2,  and  consists  of  a  crucible  A  of 
graphite  or  similar  refractory  material,  and  of  two  rods,  B  and  C, 
for  leading  in  the  current.  The  lower  rod  was  made  of  metal,  and 
fitted  into  the  base  of  the  crucible,  while  the  upper  was  of  carbon, 
or  a  water-cooled  metal  tube,  and  was  actuated  by  an  automatic 
regulating  device  to  maintain  the  arc  E  of  a  constant  length.  The 
metal  to  be  melted  was  placed  in  the  crucible,  making  electrical 
contact  with  the  lower  pole  C  ;  then  the  rod  B  was  lowered  until 
an  arc  was  started  between  this  rod  and  the  metal  in  the  crucible. 


Fig.  2.  —  Siemens'  Vertical  Arc  Furnace. 

In  the  illustration  the  metal  is  shown  melted,   at  D,  as  it  would 
be  at  the  end  of  the  operation. 

The  positive  pole  is  always  hotter  than  the  negative  pole,  and 
for  this  reason  the  metal  to  be  melted  is  made  the  positive  pole  of 
the  arc.  A  lid,  F,  was  provided  with  a  hole  for  observing  the 
operation,  or  making  additions  to  the  charge,  and  a  protecting 


W. 


Siemens'  English  patent,  2,110,   1879,   see  Borchers'  Electric   Smeltin 


HISTORY.  5 

covering,  G,  was  arranged  to  reduce  as  far  as  possible  the  radia- 
tion of  heat  from  the  crucible.  • 

In  this  furnace  he  was  not  only  able  to  melt  several  pounds 
of  steel  and  platinum,  but  even  to  vaporize  copper  which  had 
been  packed  with  carbon  in  the  crucible.* 

Siemens  also  invented  a  furnace  having  horizontal  electrodes, 
as  shown  in  Fig  3.t  In  this  furnace  the  arc  passes  between  the 
two  electrodes  B  and  C,  and  heats,  by  radiation,  the  material  con- 
tained in  the  crucible.  In  both  furnaces  he  provided  water-cooled 
copper  electrodes  for  the  negative  pole  of  the  arc,  to  avoid  the 
wasting  that  takes  place  when  carbon  electrodes  are  used.  In 
Fig.  3,  the  negative  electrode,  C,  consists  of  a  copper  tube,  closed 
at  one  end,  and  cooled  by  water,  which  is  introduced  by  a  smaller 


Fig.  3. — Siemens'  Horizontal  Arc  Furnace. 

pipe  inside  it.  The  positive  electrode,  B,  is  a  hollow  carbon  rod, 
and  through  it  a  neutral  or  reducing  gas,  can  be  introduced  into 
the  furnace. 

In  1883,  Faure  patented  an  electric  furnace  of  the  resistance 
type,  the  heat  being  generated  by  the  passage  of  the  current 
through  solid  conducting  rods  imbedded  in  the  hearth  of  the 
furnace,  on  the  same  principle  as  the  electric  cooking  stove. 

The  resistance  type  of  electric  furnace  was  made  a  com- 
mercial success  by  the  brothers,  E.  H.  and  A.  H.  Cowles,  whose 


*Siemens  and  Huntingdon,  British    Assoc.    for   the   Adv.   of  Science,  1882,  pp.    496-8. 
f\V.   Siemens'   English  patent,  4,208,  1878,  see  Borchers'  Electric  Smelting. 


e  THE     ELECTRIC     FURNACE. 

inventions  were  described  in  1885.*  Their  furnace  was  heated  by 
passing  an  electric  current  through  coarsely  powdered  charcoal 
or  gas&carbon.  This  new  method  was  used  for  a  variety  of  pur- 
poses,' one  of  these  being  the  production  of  aluminium  alloys  by 
heating  a  mixture  of  alumina  and  carbon  with  copper  or  some 
other  alloying  metal. 

Fig.  4  represents  the  Cowles  furnace  for  aluminium  alloys.  It 
consists  of  a  rectangular  brick  chamber  fitted  with  inclined  carbon 
electrodes,  A  and  B,  and  filled  with  the  mixture  of  alumina,  carbon 
and  copper.  The  electric  current  flows  between  the  electrodes 
through  some  pieces  of  retort  carbon,  C,  and  thus  heats  the 
charge,  which,  when  heated,  carries  part  of  the  current.  The 
gases  resulting  from  the  chemical  reaction  escape  and  burn  at  D, 
and  the  molten  alloy  collects  at  the  bottom  of  the  furnace. 

In  1886,  Hall,t  and  Heroultt  patented  processes  for  the  pro- 
duction of  aluminium,  and  their  processes,  as  now  used,  consist 


Fig.  4. — Cowles'  Furnace  for  Aluminum  Alloys. 

keeps  the  material  fused. 

in  passing  an  electric  current  through  fused  compounds  of 
aluminium ;  the  electrolytic  action  of  the  current  liberates  the 
aluminium  from  these  compounds,  and  the  heat  of  the  current 
Fig.  5  may  be  considered  to  represent  either  the  Hall  or  the 
Heroult  furnace.  Each  of  these  consists  of  an  iron  tank,  A,  lined 
with  carbon,  B,  and  provided  with  a  number  of  carbon  rods,  C, 

*Dr.  T.  Sterry  Hunt,  Amer.  Inst.  Min.  Eng.  (Sept.  16,  1885),  vol.  xiv.,  p.  492.  Prof. 
C.  F.  Mabery,  Amer.  Assoc.  for  the  Adv.  of  Science  ;  Aug.  28,  1885,  vol.  xxxiv., 
p.  136.  E.  II.  and  A.  H.  Cowles,  U.S.  patents,  319,795  (1884),  see  Borchers' 
Electric  Smelting;  and  324,658  and  324,659  (1885),  see  Richards'  Aluminium. 

fC.  M.  Hall,  U.S.  patents  400,766  and  400,664,  April  2,  1889  (applied  for  July  o 
1886),  see  Richards'  Aluminium. 

tPaul  Heroult,  French  patents,  175,  711,  April  23,  1886,  and  170,003,  April  15,  1887, 
see  Richards'  Aluminium. 


HISTORY. 


which  dip  into  the  fused  electrolyte,  E,  contained  in  the  tank. 
The  carbon  rods  are  made  the  positive  and  the  tank  the  negative 
electrode.  The  electrolyte  consists  chiefly  of  cryolite,  and 
alumina — the  purified  ore  of  aluminium — is  added  at  intervals. 
The  electrolytic  action  of  the  current  splits  up  the  alumina 
into  aluminium  and  oxygen ;  the  former  collects  in  the  fused  state 
at  the  bottom  of  the  tank,  while  the  latter  is  liberated  in  contact 
with  the  carbon  rods,  and  consumes  them,  the  loss  of  carbon  be- 
ing about  equal  in  weight  to  the  aluminium  produced. 

It  will  be  noticed  that, 
while  the  apparatus  resembles 
Siemens'  vertical  arc  furnace 
in  general  appearance,  no  arc 
is  formed  in  this  case.  The 
current  flows  through  the 
electrolyte  from  the  carbon 
rods  to  the  melted  aluminium, 
and  in  doing  so  produces 
enough  heat  to  keep  the 
cryolite  in  a  state  of  fusion,  at 
a  temperature  of  nearly  9OO°C. 
(i,6oo°F.). 

Fig.  5. — Aluminium  Furnace.  All  the  aluminum  at  present 

produced      comes      from      the 

electric  furnace.  During  the  year  1905  the  output  of  aluminium  in 
the  United  States  alone  amounted  to  10,000,000  pounds  ;*  where- 
as, in  1885 — before  the  electrical  process  was  invented — it  was 
only  283  pounds. 

The  next  stage  in  the  history  of  the  electric  furnace  is  marked 
by  the  classical  experiments  and  researches  of  Henri  Moissan. t 
These  researches  were  commenced  in  1892,  and  had  for  their 
objective  the  manufacture  of  artificial  diamonds.  Moissan  worked 
in  accordance  with  scientific  method,  and,  although  his  researches 
were  not  conducted  with  a  view  to  technical  results,  his  unique 
experiments  have  given  a  great  impetus  to  the  commercial  use  of 
the  electrical  furnace,  as  well  as  establishing  on  a  scientific  basis 
our  knowledge  of  chemistry  at  the  high  temperatures  used  in  the 
electric  furnace. 


•Mineral    Industry,   vol.    xiv.,   p.    n. 

fH.   Moissan,  Description  d'un  nouveau  four  electrique,  Comptes  Rendos  de  1'Acad 
des    Sciences,    vol.    cxv.,   p.    1031,   Dec.,    1892. 

H.    Moissan,    Le    Four    Electrique,    Paris,    1897. 

II.    Moissan,  The  Electric  Furnace;  «rans.   by  Victor  Lenher,   1904. 


8  THE     ELECTRIC     FURNACE. 

Fig.  6  indicates  the  type  of  furnace  he  usually  employed. 
It  consists  of  two  blocks  of  limestone,  A  and  B,  and  two  carbon 
rods,  C  and  D,  to  which  the  electrical  connections  are  made.  A 
cavity  is  hollowed  out  in  these  blocks,  and  the  material  to  be 
heated  is  placed  in  a  crucible,  E,  of  carbon  or  magnesia.  As  even 
lime  melts  and  volatilizes  at  the  temperature  of  this  furnace,  a 
lining  of  alternate  layers  of  carbon  and  magnesia  was  arranged 
as  shown  in  the  figure,  in  order  to  withstand,  as  far  as  possible, 
the  heat  of  the  arc. 

In  some  of  these  experiments  Moissan  converted  two  or  three 
hundred  electrical  horse-power  into  heat  in  a  furnace  of  only  a  few 


Fig.  6. — Moissan's  Furnace. 


inches  internal  dimensions.  At  the  enormously  high  temperature 
of  his  furnace  everything  melts  or  turns  to  vapor.  Carbon  is  the 
most  refractory  substance  known,  and  even  that  turns  to  graphite 
and  volatilizes ;  magnesia,  another  very  refractory  substance, 
melts  at  the  highest  temperature  of  the  furnace  and  vaporizes. 
Lime,  quartz,  and  alumina  all  melt  and  boil  in  the  furnace.  Gold, 
copper,  iron,  and,  in  fact,  all  the  metals  can  also  be  melted  and 
boiled  in  the  electric  furnace. 

An  improved  form  of  the  Moissan  furnace*  has  recently  been 
described,  in  which  an  electric  current  of  1,000  amperes  at  from, 
50  to   150  volts  is  employed.      In  the  case  of  direct  current  this 
would  mean  70  to  200  horse-power,  and,  while  this  is  not  quite  as 


*Engineering,   March   23,   1906,  vol.    Ixxxi.,   p.    381. 


HISTORY.  9 

much  as  Moissan  sometimes  used,  it  is  more  than  is  often  avail- 
able for  scientific  experimental  work.  In  such  a  furnace  it  is 
easy  to  produce  a  temperature  more  than  double  that  usually 
obtainable  by  the  combustion  of  fuel,  and  it  is,  therefore,  an  in- 
valuable apparatus  in  the  hands  of  the  metallurgist  and  the 
chemist. 

Moissan  also  experimented  on  the  reduction  of  metals  from 
their  oxides,  and  found,  as  had,  indeed,  been  stated  by  C.  F. 
Mabery*  in  1885,  and  by  Dr.  W.  Borchers,  in  1891,  that  carbon 
will  reduce  any  metal  from  its  oxide  at  the  temperature  of  the 
electric  furnace.  Not  only  will  carbon  reduce  any  metal  from  its 
oxide,  but  at  this  high  temperature  carbon  will  also  combine  with 
the  metal  itself  to  form  a  carbide.  The  production  and  properties 
of  many  of  these  carbides  were  studied  by  Moissan. 

One  of  the  most  spectacular  of  his  experiments  was  the  pro- 
duction of  the  diamond.  This  is  a  crystallized  form  of  carbon, 
and  if  a  suitable  solvent  were  available  it  should  be  possible  to 
crystallize  carbon  as  diamonds.  Moissan  found  such  a  solvent  in 
iron  and  certain  other  metals.  In  the  electric  furnace  these 
metals  dissolve  notable  quantities  of  carbon,  and  by  cooling  them 
under  suitable  conditions  Moissan  was  able  to  obtain  some  of  the 
carbon  as  microscopical  diamonds,  which  he  isolated  by  dissolving 
the  metal  in  acids.  The  present  writer,  in  common  with  other 
experimenters,  has  repeated  this  production  of  the  diamond,  and 
has  also  seen  what  appeared  to  be  a  diamond,  which  had  been 
found  imbedded  in  a  piece  of  iron  or  steel  produced  by  ordinary 
smelting  methods. 

Although  diamonds  are  not  yet  manufactured  in  ton  lots, 
Moissan's  researches  on  the  conversion  of  carbon  into  graphite, 
and  on  the  production  of  calcium  carbide,  have  been  followed 
by  important  commercial  developments.  The  formation  of  calcium 
carbide  in  the  electric  furnace  was  independently  achieved  in  1893 
by  T.  L.  Willson,  who  developed  the  manufacture  of  the  carbide 
on  commercial  lines. t 

Fig.  7  illustrates  the  Willson  carbide  furnace,  consisting  of 
an  iron  crucible,  A,  the  base  of  which  has  a  carbon  lining,  D.  The 
crucible  is  connected  to  one  cable  from  the  dynamo  or  trans- 
former, while  the  other  cable  is  connected  to  a  large  carbon  elec- 
trode, B  C,  suspended  within  the  crucible.  The- arc  being  started 
between  C  and  D,  the  charge  of  powdered  lime  and  coke  is  fed  in 

*C.    F.    Mabery,    (loc.    cit.). 

-{•Industries  and   Iron,   1896,  vol.  xx.,   p.   322. 


10 


THE     ELECTRIC     FURNACE. 


around  C,  and  in  the  heat  of  the  arc  the  lime  is  reduced  by  means 
of  the  coke  to  the  metal  calcium,   and  this    in  turn  reacts    with 

more  coke  to  form  a  carbide. 
These  reactions  may  be  repre- 
sented by  the  following  chemical 
equations,  which  also  indicate 
the  relative  amounts  of  lime  and 
coke  to  use  in  the  charge : — 


Fig.  7.  —  Willson's  Carbide 
Furnace< 


The  calcium  carbide,  when 
formed,  is  fusible  at  the 
temperature  of  this  furnace,  and 
forms  a  pool  beneath  the  elec- 
trode, B  C,  and  by  gradually 
raising  this  electrode,  a  mass  of 
carbide  is  built  up.  When  the 
crucible  is  nearly  filled,  the 
operation  is  stopped  and  the 
crucible  allowed  to  cool  before 
turning  out  the  block  of  carbide. 


The  carbonic  oxide  produced  by 
the  reaction  escapes  and  burns  in  the  upper  part  of  the  crucible,, 
as  is  indicated  in  Fig.  7.  Many  other  forms  of  carbide  furnaces 
have  been  devised,  and  are  now  being  operated  on  a  large  scale, 
some  of  these  being  intermittent,  like  the  Willson  furnace,  whilst 
others  are  continuous  in  action.  The  World's  production  of 
calcium  carbide  in  1904  amounted  to  90,000  tons.  The  value  of 
calcium  carbide  depends,  as  is  well  known,  upon  the  ease  with 
which  it  acts  upon  water  to  form  the  valuable  illuminating  gas,. 
acetylene. 

Another  important  carbide,  produced  in  the  electric  furnace, 
is  carborundum,  a  carbide  of  silicon,  SiC.  The  discovery  of  car- 
borundum by  E.  G.  Acheson  in  1891  is  described  by  himself  in  an 
interesting  lecture  on  "Discovery  and  Invention."*  Mr.  Acheson 
was  Attempting  to  harden  clay  by  impregnating  it  with  carbon  in 
an  improvised  electric  furnace.  After  the  experiment  he  noticed 
a  few  bright  specks  at  the  end  of  the  carbon  electrode.  These 
specks  were  found  to  be  hard  enough  to  cut  not  only  glass,  but 


*The  Electric   Journal,  Pittsburgh,   1906. 


HISTORY. 


I  I 


even  the    diamond  itself,   and  were  the  origin  of    the  important 
carborundum  industry. 

Carborundum  is  made  by  placing  a  mixture  of  sand  and  coke 
with  smaller  amounts  of  sawdust  and  salt  in  a  firebrick  chamber, 
and  passing  an  electric  current  through  a  core  of  carbon  placed 
in  the  middle  of  the  charge.  The  sand,  in  the  charge,  becomes 
reduced  to  silicon,  and  combines  with  carbon  to  form  car- 
borundum, which,  at  the  high  temperature  (over  2,ooo°C.)  of  the 
furnace,  assumes  a  beautiful,  iridescent,  crystalline  form,  and  is 
of  such  extreme  hardness  that  it  has  proved  to  be  a  very  valuable 
abrasive.  It  is  now  widely  used  as  a  grinding  agent  in  the  metal 
trades  and  other  industries,  and  it  is  also  useful  as  a  refractory 
lining  for  electric  and  other  furnaces,  and  as  a  deoxidizing  addi- 
tion in  the  manufacture  of  steel. 


r     f     t      f     f     T     f     f 


Fig.  8.  —  Acheson's  Carborundum  Furnace. 

The  furnace  employed*  is  shown  in  Fig.  8,  and  consists  of 
two  permanent  end  walls,  A  and  B,  which  support  large  bundles 
of  carbon  rods,  C  and  D,  in  heavy  bronze  'holders.  The  current  is 
carried  between  C  and  D  by  a  core  of  broken  carbon,  E,  and  as  the 
charge  does  not  fuse,  this  core  remains  in  position  until  the  end 
of  the  operation.  A  layer  of  brilliant  graphite  was  usually  found 
between  the  core  and  the  crystalline  carborundum.  This  graphite 
resulted  from  the  decomposition  of  the  carbide  in  the  hottest  part 
of  the  furnace.  From  this  observation  Acheson  evolved  the 
artificial  production  of  graphite,  which  he  patented  in  1896.  t  It 
consists  in  heating  coke,  anthracite  or  other  form  of  carbon  con- 
taining a  small  amount  of  iron  oxide  or  certain  other  substances. 


*The  Carborundum   Furnace,  F.  A.  J.  FitzGerald.     Electrochemical  Industry,  vol.  iv., 

p.    53,    1906. 
fThe  Conversation  of  Amorphous  Carbon  to  Graphite,  F.  A.  J.  FitzGerald,  Journal 

of  the    Franklin    Institute,    Nov.,    1902. 


12  THE     ELECTRIC     FURNACE- 


The  iron  and  other  impurities  in  the  carbon  are  volatilized  at  the 
high  temperature  of  the  electric  furnace  and  leave  the  carbon 
very  pure  and  converted  into  graphite.  As  much  as  1,000  electrical 
horse-power  is  consumed  in  one  of  these  furnaces,  producing  a 
temperature  of  over  2,2oo°C. 

The  manufacture  of  carborundum,  graphite,  siloxicon  and 
other  products  of  the  Acheson  electric  furnaces  at  Niagara  is  more 
fully  described  in  Chapter  vi. 

Calcium  carbide  has  been  one  of  the  most  important  products 
of  the  electric  furnace,  and  its  manufacture  still  consumes  more 
electrical  power  than  that  of  any  other  product.  It  was  a  financial 
crisis  in  the  carbide  industry  that  led  to  the  electric  smelting  of 
iron,  steel,  and  the  other  iron  alloys.* 

A  few  years  ago  the  production  of  calcium  carbide  became 
larger  than  the  demand,  and  this  forced  some  manufacturers  to 
turn  their  attention  to  other  methods  of  utilizing  their  electric 
furnaces.  With  this  object  experiments  were  made  in  France 
and  elsewhere  about  the  year  1900  on  the  production  of  ferro- 
chrome,t  ferro-silicon,  and  the  other  ferro  alloys  ;  and  these  ex- 
periments were  so  successful  that  not  only  have  the  new  processes 
been  able  to  compete  with  existing  methods,  but,  in  the  case  of 
ferro-chrome  at  any  rate,  the  electric  product  has  captured  the 
market. 

The  ferros  are  alloys  of  iron,  with  manganese,  chromium, 
silicon,  or  some  other  metal,  and  they  usually  contain  a  notable 
amount  of  carbon,  being,  in  fact,  cast  iron,  in  which  part  of  the 
iron  has  been  replaced  by  another  metal.  Some  of  these  are 
used  in  the  production  of  open-hearth  and  Bessemer  steel,  and 
others  for  the  production  of  special  alloy  steels.  Ferro-nickel, 
ferro-tungsten,  ferro-titanium  and  ferro-molybdenum  have  also 
been  employed  in  steel  making. 

The  carbide  furnaces,  which  were  lined  with  carbon,  were 
satisfactory  for  the  production  of  these  carburized  materials,  but 
certain  changes  were  necessary  before  they  could  be  used  for  the 
manufacture  of  steel.  In  France,  Heroult,|  and  in  Sweden, 
Kjellin§  succeeded  in  adapting  the  furnace  to  the  production  of 


*Albert   Keller,    The    Application    of    the    Electric    Furnace     in    Metallurgy,     Journ. 

Iron    and    Steel    Inst.,    1903,    No.    I.,   p.    161. 
•f-Ibid,   pp.    162    and   166-169. 
JHeroult    Steel    Furnace.      Electrochemist    and    Metallurgist,    vol.    i.    (1901),    p.     196, 

Electrochemical   Industry,  vol.   i,   (1902-3),   pp.   63,  287,   449. 
gKjellin    Steel    Furnace.      Electrochemist    and    Metallurgist,    vol.    i.    (1901),    p.     90; 

Electrochemical   Industry,   vol.    i.    (1902-3),    pp.    141,    376,    462,   576. 


HISTORY.  13 

good  quality  steel  from  scrap  steel,  pig  iron,  etc.  ;  and  good 
crucible  and  special  alloy  steels  have  for  some  years  been  pro- 
duced commercially  in  the  electric  furnace.  The  original  patents 
of  these  pioneers  of  electric  steel-making  were  taken  out  about 
the  year  1900,*  just  one  hundred  years  after  the  discovery  of  the 
voltaic  battery. 

The  origin  of  the  electric  smelting  of  iron  ores  was,  however, 
somewhat  earlier  than  this.  In  the  year  1898  Captain  Stassano,t 
in  Italy,  patented  his  electrical  furnace  for  smelting  iron  ores,  and 
in  the  following  year  demonstrated  the  working  of  his  process. 
Quite  a  sensation  was  produced  by  his  experiments,  as  although 
it  was  not  surprising  to  learn  that  iron  ores  could  be  smelted  by 
electricity,  the  ordinary  price  of  electric  power  was  so  high  that  it 
appeared  preposterous  to  attempt  to  use  it  in  competition  with 
coke  in  the  blast  furnace. 

It  is  a  matter  of  general  knowledge  that  the  retail  price  of 
any  commodity  is  higher,  and  sometimes  even  several  times  as 
high  as  the  wholesale  price,  or  the  cost  of  production ;  but  it  was 
probably  not  generally  realized  until  quite  recently  that  the  small 
consumer  of  electric  light  pays  about  one  hundred  times  as  much 
for  electricity  as  the  actual  cost  of  producing  it  from  a  good  water- 
power.  This  enormous  difference  had  given  an  exaggerated  idea 
of  the  costliness  of  electrical  power,  and  was,  no  doubt,  largely 
responsible  for  the  skepticism  with  which  Stassano's  early  ex- 
periments were  received.  These  experiments  of  Stassano, 
although  not  as  yet  commercially  successful,  have,  no  doubt,  im- 
pressed on  many  minds  the  financial  possibility  of  electric  smelt- 
ing in  general,  and  a  large  crop  of  such  processes  has  followed. 

Some  other  furnaces  suitable  for  smelting  iron  ores  are  those 
of  Keller,  Heroult  and  Harmet,  which  are  described  and  illustrated 
in  Chapter  v. 

In  view  of  the  great  importance  to  Canada  of  developing  the 
electric  smelting  of  iron  ores,  the  Canadian  Government  appointed 
in  1903  a  Commission  under  Dr.  Haanel  to  report  on  the  electro- 
thermic  processes  for  the  smelting  of  iron  ores  and  the  making 
of  steel  in  operation  in  Europe.  The  Commission  visited  Europe 
in  1904  and  saw  the  Heroult,  Keller  and  Kjellin  furnaces  in  com- 
mercial operation  making  steel  and  ferro  alloys.  At  Dr.  Haanel's 


*The    Colby    induction    steel    furnace    was    patented    in    1890.      See    Electrochemical 

Industry,  vol.  iii.  (1905),  p.  299,  and  vol.  v.   (1907),  p.  232. 
f Stassano   Steel   Furnace.      Electrochemist    and   Metallurgist,   vol.   i.    (1901),   p.    230; 

Electrochemical    Industry,    vol.    i     (1902-3),    pp.    247,    363. 


14  THE     ELECTRIC     FURNACE. 

request  the  production  of  pig  iron  from  the  ore  was  also  demon- 
strated in  the  Heroult  and  Keller  furnaces.  A  voluminous  report* 
was  published  after  the  return  of  the  Commission,  and  Dr.  Haanel 
was  so  well  satisfied  with  the  possibility  of  smelting  iron  ores 
electrically  in  countries  where  coal  was  scarce  and  water-power 
was  abundant  that  he  obtained  a  further  grant  from  the  Govern- 
ment, and  with  the  help  of  Paul  Heroult  carried  out  a  series  of 
experiments  during  the  spring  of  1906  at  Sault  Ste.  Marie  on  the 
electric  smelting  of  Canadian  iron  ores.t  As  a  result  of  these 
experiments  plants  for  the  commercial  smelting  of  iron  ores  in 
electric  furnaces  are  being  erected  at  Welland,  Ont.,  and  at  Baird 
California. 


*Report    of    the    Commission    appointed    to    investigate    the    different    electrothermic 

processes   for  the   smelting  of  iron  ores   and  the  making   of  steel  in  operation  in 

Europe.      Ottawa,    1904 
•f-Report    on    the    experiments    made   at    Sault   Ste.    Marie,    Ont.,   under    Government 

auspices   in  the   smelting   of  Canadian  iron  ores  by  the  electro-thermic  process. 

Ottawa,   1907. 


CLASSIFICATION. 


CHAPTER     II. 

DESCRIPTION    AND     CLASSIFICATION    OF     ELECTRIC 

FURNACES. 

The  Electric  Furnace  may  be  described  as  an  appliance  in 
which  materials  can  be  submitted  to  a  high  temperature  by  the 
dissipation'  of  electrical  energy.  This  definition  does  not  include 
all  cases  of  electrical  heating ;  and  with  advantage  might  be  limited 
to  the  production  of  temperatures  above  a  red  heat.  In  a  num- 
ber of  instances  such  as  the  production  of  sodium  and  aluminium, 
the  electric  current  is  required  mainly  for  isolating  the  metal  by 
electrolysis,  and  only  incidentally  for  producing  heat.  These 
processes  are  usually  considered  to  be  furnace  operations,  because 
a  high  temperature  is  produced ;  and  it  has  been  suggested,  by 
Mr.  J.  \Yright,*  that  electrolysis  should  be  classed  as  a 
furnace  process,  when  fused  anhydrous  salts  are  employed ;  ex- 
cluding the  more  familiar  electrolytic  processes  in  which  aqueous 
electrolytes  are  used. 

Heat  is  produced  whenever  an  electric  current  encounters  any 
resistance  to  its  flow ;  the  energy,  producing  the  current,  being 
transformed  into  heat.t  Even  the  best  electrical  conductors 
oppose  some  resistance  to  the  flow  of  an  electric  current,  and 
work  must  consequently  be  done  in  maintaining  the  current.  If 
an  electric  circuit  is  made,  in  part,  of  a  good  conductor  (such  as  a 
short,  stout  copper  cable)  and,  in  part,  of  a  poor  conductor  (such 


Fig.  9.— Electric  Circuit. 

as  a  thin  rod  of  carbon)  the  greater  part  of  the  heat  will  be  pro- 
duced in  the  poor  conductor,  which  may  even  become  red  hot, 
while  the  remainder  of  the  circuit  remains  cool. 

*Author   of    "Electric    Furnaces    and   Their    Industrial   Application." 
f  A   part  of  the   energy   is    sometimes   changed   into   chemical   energy   or  into    other 
forms    of  electrical  energy. 


I 6  THE    ELECTRIC     FURNACE. 

Fig.  9  represents  such  a  circuit :  D  is  a  dynamo ;  B  and  C 
are  stout  copper  wires  or  cables,  and  R  is  a  carbon  "Resistance" 
or  "Resistor;"  that  is  to  say,  an  electrical  conductor  made  of 
carbon  that  offers  a  considerable  resistance  to  the  flow  of  the  cur- 
rent. The  windings  in  the  dynamo  are  of  copper,  and  these  and 
the  cables  B  and  C  are  so  stout,  that  the  resistance  they  offer  to 
the  flow  of  the  current  is  only  small.  In  this  circuit, 
mechanical  work  is  constantly  required  to  turn  the  dynamo, 
and  this  work  is  converted  into  heat  mainly  in  the  re- 
sistor R  ;  and  to  a  less  extent  in  the  conductors  B  and  C,  and  the 
dynamo  D.  Such  an  arrangement  may  represent  an  electric  re- 
sistance furnace  operated  by  a  dynamo.  The  work  spent  in  driv- 
ing the  dynamo,  is  converted  into  heat,  and  by  giving  to  the 
furnace  a  far  higher  resistance  than  that  of  the  remainder  of  the 
circuit,  we  can  obtain  nearly  all  the  heat  in  the  furnace ;  only  a 
small  proportion  being  wasted  in  the  dynamo  and  conducting 
cables.  The  amount  of  heat  developed  depends  upon  the  strength 
of  the  electric  current,  as  well  as  on  the  amount  of  resistance  it 
meets.  By  increasing  the  furnace  resistance,  the  current  is  de- 
creased;  consequently,  beyond  a  certain  point,  less  heat  will  be 
developed  in  the  furnace. 

An  electric  current  is  measured  in  "amperes,"  the  electrical 
pressure  producing  the  current  is  measured  in  "volts,"  and  the 
electrical  resistance  of  a  conductor  is  measured  in  "ohms." 
Using  these  units,  the  electric  current  flowing  around  a  circuit 
is  equal  to  the  electrical  pressure  or  E.M.F.  (electro-motive-force) 
driving  it,  divided  by  the  electrical  resistance  of  the  circuit. 

When  an  electric  current  flows  through  a  resistpr,  as  in  Fig. 
9,  the  amount  of  heat  produced  is  proportional  to  the  resistance, 
and  to  the  square  of  the  current;  or,  to  the  E.M.F.  and  the  cur- 
rent. Taking  as  a  unit  the  heat  that  wrould  raise  the  temperature 
of  one  gram  of  waiter  from  o°C.  to  i°C.,  it  is  found  that— 

H  r=  o.24C2  R  t  =  0.24  E  C  t, 
where, — 

H  — heat  produced  in  gram  centigrade  units, 

C  — current  in  amperes, 

R  — resistance  in  ohms 

E  -  electro-motive-force  in  volts, 

t  =  time  in  seconds. 

In  the  circuit  shown  in  Fig.  9  the  current  C  would  be 
measured  in  amperes  by  means  of  an  ammeter,  A,  placed  in  one 
of  the  cables;  the  E.M.F.,  E.,  in  volts  by  means  of  a  voltmeter, 


CLASSIFICATION.  I/ 

V,  connected  to  the  terminals  of  the  resistor ;  and  the  resistance 
R,  in  ohms,  would  be  deduced  from  the  relation — CR  =  E.  The 
above  considerations  are  only  exact  in  the  case  of  an  electric  cur- 
rent flowing  steadily  in  one  direction ;  in  the  case  of  alternating 
currents  a  sort  of  electrical  inertia  is  observed  which  modifies 
these  results. 

In  the  arc  furnace,  the  electric  current  encounters  not  only  an 
inert  resistance,  but  also,  an  opposing  electrical  force.  Both  the 
resistance  and  the  opposing  electrical  force  cause  the  energy  of 
the  current  to  be  turned  into  heat,  and  to  contribute  to  the  heating 
of  the  furnace.  A  similar  opposing  electrical  force  is  present  in 
an  electrolytic  furnace,  such  as  is  used  for  the  production  of 
aluminium.  In  the  latter  case,  however,  the  work  done  in  over- 
coming this  force,  is  turned  into  chemical  energy  (the  isolating  of 
aluminium  from  alumina)  instead  of  into  heat.  In  most  furnace 
operations,  chemical  and  physical  changes  are  produced,  and 
these  increase  or  diminish  the  amount  of  heat  liberated  in  the 
furnace. 

An  electric  furnace  consists  of  the  following  essential  parts 
and  accessories: —  . 

in  Some  conducting  material  heated  by  the  passage  of  the 
current.  This  may  be  a  vapor,  as  in  the  electric  arc ;  or  a  solid, 
such  as  coke ;  or  a  liquid,  such  as  molten  slag  or  molten  steel. 

(2)  An  envelope  of  refractory  material.    The  walls,  floor  and 
roof  of  a  furnace  are  needed  to  conserve  the  heat,  to  retain  the 
charge,  to  exclude  the  air  and  to  support  the  electrodes  and  the 
charging  and  discharging  apparatus. 

(3)  Electrodes,  or  conductors  for  bringing  the  current  into 
the  furnace,  carbon  rods  are  usually  employed  for  this  purpose. 
They  are  subjected  to  the  heat  of  the  furnace  at  one  end,  and  at 
the  other  end    must   be     sufficiently   cool     to  permit   of     making 
electrical    contact   by   means   of  special    holders   with  the   cables 
bringing  the  current  to  the  furnace.     In  some  furnaces  electrodes 
are  not  needed,  the  current  being  generated  by  induction  in  the 
furnace  itself. 

(4)  Electrode  holders. — These  are  usually  metal  clamps  for 
holding  and  making  electrical  contact  with  the  carbon  electrodes  ; 
provision  being  made  for  preventing  the  excessive  heating  of  the 
holder. 

(5)  Charging  and  discharging  facilities. — Some  furnaces  are 
intermittent    in   action,    the   charge    being    added,    heated    in    the 
furnace  and  then  removed,  before  the  fresh  charge  can  be  intro- 
duced.       Other  furnaces  are  continuous  in  action,   involving  the 


]8  THE     ELECTRIC     FURNACE. 

periodic,  or  continuous  additions  of  the  raw  material,  and  removal 
of  the  products. 

Apart  from  the  furnace  itself,  the  following  operating  factors 
have  to  be  considered : — 

(6)  Source  of  electric  current. — The  electric  current  is  pro- 
duced by  means  of  a  dynamo,  and  as  it  is  usually  supplied  at  a 
higher  voltage  than  is  suitable  for  the  furnace,  a  transformer  may 
be  required  to  reduce  the  voltage ;   the  amount  of  current  being 
simultaneously  increased  almost  proportionately  to  the  reduction 
in  the  voltage.     The  current  may  be  alternating,  or  direct,  but  an 
alternating  current  is  usually  preferred,  as  it  can  be  transformed 
more  readily    from  one  voltage  to    another.        In    cases    where 
electrolysis   is    required,    as    in    the  production    of    aluminium   or 
sodium,  the  direct  current  can  alone  be  used. 

(7)  Cables,  measuring  instruments,  and  regulating  devices. 
Cables  are  used  for  bringing  the  electric  current  from  the  trans- 
former or  dynamo  to  the  furnace.       Measuring  instruments,  such 
as  ammeters,  voltmeters  and  wattmeters  are  used  for  measuring 
and    recording   the   current,    electro-motive-force     and     electrical 
power  supplied  to  the  furnace.     Regulating  devices  are  required 
for  advancing  the  electrodes  as  they  are  consumed  in  the  furnace, 
and    for  regulating  by   this    means,   or  in   some   other   way,    the 
amount  of  current  flowing  through  the  furnace. 

Classification. 

The  usual  classification  of  electric  furnaces  depends  primarily 
upon  the  nature  of  the  resistor  used  to  develop  the  heat.  Thus 
there  are  arc  furnaces,  in  which  the  heat  is  developed  in  the  electric 
arc;  and  resistance  furnaces,  in  which  the  heat  is  developed  by  the 
passage  of  the  current  through  a  solid  or  liquid  resistor.  The 
classification  may  depend,  also  upon  the  manner  in  which  the  heat 
is  transmitted  to  the  charge ;  thus  in  arc  furnaces  the  heating  may 
be  direct,  as  in  Siemens'  vertical  arc  furnace,  in  which  the  metal 
to  be  melted  forms  one  pole  of  the  arc ;  or  indirect,  as  in  his  hori- 
zontal arc  furnace,  where  independent  electrodes  are  employed, 
and  in  which  the  heat  is  transmitted  from  the  arc  to  the  charge 
by  radiation  and  conduction. 

In  resistance  furnaces  the  charge  to  be  heated  may  itself  con- 
stitute the  resistor,  or  else  an  independent  resistor  may  be  em- 
ployed. The  latter  nearly  always  consists  of  a  solid  core,  usually 
of  carbon,  and  it  may  be  surrounded  by  the  charge  that  is  to  be 
heated,  or  imbedded  in  the  walls  of  the  furnace.  A  charge  that 


CLASSIFICATION.  IQ 

is  to  be  heated  directly  by  the  passage  of  the  current,  may  be 
either  solid  or  liquid,  and  in  the  case  of  a  liquid  charge,  the 
electric  current  may  produce  heat  merely,  or  may  also  produce 
electrolysis. 

The  following  classification  is  based  on  these  considerations, 
and  includes  examples  of  each  class. 

Arc  Furnaces. 

The  heat  is  produced  by  one  or  more  electric  arcs. 


Fig.  10. — Independent  Arc  Furnace. 

(1)  Independent  arc  furnaces. — The  arc  is  independent  of  the 
charge  to  be  heated ;  being  formed  between  two  or  more  movable 
electrodes.        The   charge   is   heated  by   radiation   from   the   arc, 
which   is   usually  horizontal. 

Fig.  10  shows  such  a  furnace,  consisting  of  a  refractory 
chamber,  A.B.,  in  wrhich  an  arc,  E,  is  formed  betwreen  the  movable 
carbon  electrodes  C  and  D ;  the  material  to  be  heated  being 
shown  melted  at  F. 

Moissan's  furnace,  Fig.  6,  Siemens'  horizontal  arc  furnace, 
Fig.  3,  and  Stassano's  steel-making  furnace  are  examples  of  this 
class.  The  Stassano  furnace,  Fig.  37,  p.  130,  consists  of  a 
chamber  lined  with  magnesia  bricks,  and  provided  with  three 
carbon  electrodes,  between  which  a  three  phase  arc  plays.  The 
ore  or  other  material  is  placed  in  the  chamber  below  the  level  of 
the  arc,  and  is  heated  by  radiation. 

(2)  Direct  heating  arc  furnaces. — The  charge  in  the  furnace 
forms  one  pole  of  the  arc  and  is  thus  heated  directly  as  well  as  by 
radiation.     The  arc  is  usually  vertical. 


2O 


THE     ELECTRIC     FURNACE. 


Fig.  ii  represents  an  arc  furnace  in  which  the  material  D,  to 
be  heated,  forms  one  pole  of  the  arc.  A  is  a  chamber  lined  with 
refractory  material,  and  B  and  C  are  the  two  electrodes  :  the  upper 
one,  B,  is  movable;  the  lower,  C,  is  fixed,  forming  part  of  the 
bottom  of  the  furnace,  and  making  electrical  contact  with  the 
charge  D.  The  furnace  is  started  by  lowering  B  until  it  touches 
D,  thus  allowing  the  current  to  pass.  B  is  then  raised,  forming 
an  electric  arc  between  B  and  D. 

Siemens'  vertical  arc  furnace,  Fig.  2,  Willson's  carbide 
furnace,  Fig.  7,  and  Heroult's  steel  furnace,  are  examples  of  this 


Fig.  11. — Direct  Heating  Arc  Furnace. 

class.  The  Heroult  steel  furnace,  Fig.  23,  p.  87,  consists  of  a 
chamber  for  containing  the  molten  steel,  with  two  vertical  carbon 
rods  dipping  through  holes  in  the  roof.  An  arc  is  formed  between 
each  carbon  rod  and  the  fused  charge ;  the  current  entering 
through  one  rod,  passing  through  the  melted  steel  and  slag,  and 
returning  through  the  other  rod.  Furnaces  of  this  class  are  rather 
less  convenient  for  scientific  investigations  than  the  independent 
arc  furnace  ;  because  the  temperature  is  less  easy  to  regulate,  the 


CLASSIFICATION. 


21 


arc  is  more  difficult  to  control  (when  the  charge  consists  of  cold 
metal),  and  the  carbon  of  the  electrodes  is  apt  to  affect  the  chemical 
composition  of  the  charge.  On  the  other  hand,  the  heat  is 
transmitted  more  directly,  thus  obtaining  a  greater  economy,  and 
only  one  movable  electrode  is  needed  for  each  arc. 

Resistance    Furnaces. 

In  these,  the  heat  is  produced  by  the  passage  of  the  electrical 
current  through  some  solid  or  liquid  resistor.  They  may  be 
divided  into  two  main  classes,  in  one  of  which  a  special  resistor  is 
provided,  and  in  the  other  the  charge  itself  constitutes  the  resistor. 
The  second  class  may  be  subdivided  into  two  classes ;  in  one  of 
these  the  current  is  used  merely  to  heat  the  charge,  while  in  the 
other  it  also  produces  electrolysis  of  the  fused  contents  of  the 
furnace.  These  will  be  treated,  for  convenience,  as  three  inde- 
pendent classes. 

I. — Furnaces  With  Special  Resistor. 

The  resistor  is  a  solid,  and  is  imbedded  in  the  walls  of  the 
furnace,  or  in  the  charge  .itself. 


Fig.  12.— Electrical  Tube  Furnace. 

(i)     Furnaces  with  the  resistor  imbedded  in  the  walls.    The 

furnace  shown  in  Fig.  12  may  be  taken  as  an  example,  it  consists 
of  a  tube  T,  often  of  porcelain,  a  spiral  of  platinum  wire,  and  a 
heat  retaining  envelope  or  covering.  An  electric  current  passes 
through  the  wire  and  heats  it  to  any  desired  temperature  below  its 
melting  point,  I775°C.,  or  3227^.,  and  ultimately  the  tube  and  its 
contents  may  be  heated  nearly  to  the  same  temperature.  The 
substance  to  be  heated  is  placed  in  the  tube  T.  This  arrange- 
ment is  convenient  for  heating  a  material  in  any  particular  gas, 
and  for  observing  the  operation ;  as  this  can  be  done  through  glass, 
3 


22 


THE     ELECTRIC     FURNACE. 


or  mica  windows  at  the  ends  of  the  tube.  Provision  must  be 
made  for  preventing'  the  displacement  and  short  circuiting  of  the 
coils  of  wire  when  expanded  by  the  heat.  The  temperature  that 
can  be  attained  in  this  furnace  depends  upon  the  refractory  quali- 
ties of  the  tube,  and  envelope,  as  well  as  on  the  melting  point  of 
the  platinum  itself,  and  in  practice,  the  temperature  attained 
would  be  far  short  of  the  melting  point  of  the  platinum  wire.'* 

This  furnace  is 
very  convenient  for 
laboratory  experiments 
on  a  small  scale,  and 
at  moderate  tempera- 
tures, but  its  use  is  re- 
stricted by  the  high 
price  of  platinum. t  A 
somewhat  similar  fur- 
nace in  which  the  use 
of  platinum  has  been 
avoided  is  shown  in 
Fig.  13,  which  repre- 
sents in  sectional  ele- 
vation, and  in  plan 
with  the  cover,  B,  re- 
moved—  a  small  elec- 
trical crucible  furnace, 
constructed  at  McGill 
University,  and  intend- 
ed for  melting  small 
quantities  of  metals.  It 
could,  however,  be 
made  considerably- 

larger,  and  be  used 
for  brass  or  steel  melt- 
ing. The  furnace  con- 
sists of  two  fire  clay 
blocks  A  and  B,  a 
A  receptacle  is  formed 


Fig.  13. — Electric  Crucible  Furnace. 

crucible  C.  and  carbon  electrodes  D  and  E. 


*A  furnace,  in  which  a  crucible  of  fused  quartz  is  siirrounded  by  heating  coils 
nf  platinum  strip,  has  been  patented  by  W.  H.  Bristol,  Electrochem,  Ind.,  vol.  v.,  p.  55. 

•j-These  furnaces  can  be  obtained  in  several  forms  from  dealers  in  chemical 
apparatus.  A  furnace  suitable  for  heating  a  small  crucible  is  described  by  Prof.  H. 
M.  Howe  in  his  "Metallurgical  Laboratory  Notes,"  p.  37. 


CLASSIFICATION.  23 

in  the  block  A  to  contain  the  crucible  and  electrodes,  and  broken 
coke,  F,  is  packed  around  them.  The  current  passes  from  D  to 
E  through  the  coke,  which  becomes  hot  and  heats  the  crucible  and 
its  contents.  The  temperature  can  be  regulated  by  a  rheostat  in 
series  with  the  furnace.  The  whole  furnace  is  enclosed  in  a  metal 
box  with  a  thick  asbestos  lining  to  prevent  loss  of  heat.* 

Furnaces  of  this  type  can- now  be  made  more  satisfactorily  by 
the  use  of  a  special  resisting  material  called  kryptolt  which  would 
replace  the  coke  in  the  above  description. 

The  Conleyt  ore  smelting  furnace  is  a  large  scale  example 
of  this  class.  One  form  of  the  Conley  furnace  consists  of  a  shaft 
down  which  the  ore  passes  and  of  carbon  resistors  imbedded  in  the 
walls  of  the  furnace.  The  resistors  are  heated  by  the  passage  of 
a  current,  and  communicate  their  heat  to  the  ore  passing  over 
them. 

Small  tube  furnaces  heated  by  spirals  of  platinum  wire,  are 
very  useful  for  experimental  purposes,  but  commercial  furnaces  on 
these  lines  have  been  less  successful.  This  is  mainly  on  account 
of  the  difficulty  of  maintaining  resistors  and  adjacent  parts  of  the 
furnace,  and  because,  of  the  slow  conduction  of  heat  to  the  charge, 
and  the  large  loss  of  heat  through  the  furnace  walls. 

A  rotary  electric  furnace,  the  inner  walls  of  which  serve  as 
resistors,  being  sufficiently  conducting  when  heated,  has  been 
patented  by  B.  von  Ischewsky.il 

Tube  furnaces  for  experimental  work,  in  which  the  tube  is 
composed  of  graphite,  amorphous  carbon,  or  other  conducting 
material  which  is  heated  by  the  passage  of  the  electric  current, 
have  been  employed  by  Potter, §  Harker,*  Hutton,t  Tucker,!  and 
others. 

(2)     Furnaces  with  the  resistor  imbedded  in  the  charge. — The 

resistor  is  usually  of  carbon  and  horizontal. 


"Similar    furnaces    have    been    described    by    FitzGerald,    Electrochemical    Industry, 
vol.   iii.,  pp.   55   and  135. 

•f-Kryptol,    see  p.    149. 

tConley  furnaces,  Electrochemical  Industry,  vol.  L,  D.  426,  and  vol.  ii.,  p.  424. 
|jlschewsky   furnace,   Electrochemical  Industry,   vol.   v.,  p.   141. 

§H.    N.   Potter,   Electrochemical  Industry,   vol.    i.,    pp.    187,    188   and  250;   vol.    ii.,   p. 
203;  vol.    iii.,   p.    346,  and  vol.   iv.,   p.    191. 

*J.  A.  Harker,  Electrochemical  Industry,  vol.  iii..   p.   273. 

•f-R.    S.    Hutton    and    W.    H.    Patterson,    Electrochemical    Industry,    vol.    iii.,    p.   455, 

5). 

tS.  A.  Tucker.   Electrochemical   Industry,  vol.   v.,   p.   227,   (1907). 


THE     ELECTRIC     FURNACE. 


Pig.  14. — Borchers'  Resistance  Furnace. 

The  simplest  example  is  Borchers'  experimental  resistance 
furnace,  Fig.  14,*  in  which  a  thin  pencil  of  carbon  C  is  supported 
between  stout  carbon  rods  A  and  B,  and  the  charge  to  be  heated 
surrounds  C.  The  current  flows  between  A  and  B  through  C, 
and  may  raise  the  latter  to  a  white  heat.  The  charge  serves  in 
part  as  an  envelope  to  retain  the  heat. 

Acheson's  carborundum  furnace.  Fig.  8,  is  the  most  import- 
ant example  of  this  class.  In  this  furnace  the  conducting  core  is 
composed  of  granular  carbon,  and  is  supported  and  surrounded 
by  the  material  to  be  heated.  The  furnace  is  efficient,  because 
the  heat  is  developed  in  the  midst  of  the  charge,  which  serves  to 
retain  it.  The  temperature  can  also  be  exactly  regulated  by  vary- 
ing the  current,  while  by  using  a  number  of  cores,  as  in  the 
siloxicon  furnace,  Fig.  41,  page  154,  it  is  possible  to  obtain  ;i 
fairly  uniform  temperature  throughout  a  large  portion  of  the 
charge.  On  the  other  hand,  when  the  furnace  is  in  operation,  it 
is  impossible  to  regulate  the  resistance  of  the  core,t  and  since  this 
decreases  considerably  as  the  furnace  becomes  hotter,  the  current, 
if  supplied  at  a  constant  voltage,  may  increase  during  the  work  of 
the  furnace  until  it  becomes  too  great  for  the  dynamo,  or  trans- 
former from  which  it  is  supplied  ;  thus  involving  the  use  of  special 
apparatus  for  regulating  the  voltage.  As  the  material  to  be 
heated  acts  as  an  envelope  to  retain  the  heat,  and  as  the  charge 
does  not  become  fused,  the  outer  w^alls  can  be  of  the  simplest  cle- 

*Borchers'  Electric  Smelting  and  Refining,  1897  Ed.,  Figs.  54,  55,  172.  and  Electro- 
chemical Industry,  vol.  iii.,  p.  215. 

fin  small  furnaces  of  this  type  the  resistance  of  the  core  can  be  regulated,  within 
moderate-  limits,  by  placing  weights  m  the  charge. 


CLASSIFICATION.  25 

scription ;  merely  serving  to  retain  the  charge  in  position.  This 
furnace  would  not  be  directly  applicable  in  case  the  charge  were 
to  fuse,  since  the  core  would  become  broken.  The  furnace  is 
also  essentially  intermittent  in  action,  as  the  charge  cannot  pass 
continuously  through  it,  and  on  that  account  it  is  less  efficient, 
since  it  must  be  allowed  to  cool  between  successive  operations. 
Although  a  core  is  provided  in  this  furnace  to  carry  the  current,  a 
portion  of  the  latter  is  undoubtedly  carried  by  the  charge  itself. 


Fig.  15. — Tone's  Resistance  Furnace. 

In  the  Cowles  furnace  for  aluminium  alloys,  Fig.  4,  the 
charge  becomes  partly  fused,  and  no  doubt  serves  to  carry  the 
current,  but  at  the  beginning  of  the  operation  the  current  is  carried 
by  a  carbon  core  and  so  the  furnace  may  be  included  in  this  class. 

Tone's  resistance  furnace,*  for  the  reduction  of  metals  is 
shown  in  Fig.  15.  The  central  resisting  core  C  is  placed  vertically 

*U.    S.    patent    754,122,    see   Electrochemical    Industry,    vol.    ii.,    (1904).    p    in,    and 
Wright's   "Electric  Furnace."   p.    144. 


26  THE     ELECTRIC     FURNACE. 

in  order  to  permit  of  continuous  charging,  which  would  break 
down  a  horizontal  core.  It  is  constructed  of  carbon  blocks, 
piled  upon  each  other  in  such  a  way*  as  to  obtain  a  high  electrical 
resistance.  A  and  B  are  carbon  electrodes  for  making  electrical 
connection  with  the  core.  The  charge  is  fed  in  around  C,  and  the 
reduced  and  melted  metal  flows  through  small  holes  at  the  base 
of  the  furnace  into  the  receptacles,  D  and  E. 

II. — Furnaces  without  Special  Resistor  and  without  Electrolytic 

Action. 

In  these  furnaces  the  material  to  be  heated  forms  the  resistor, 
and  may  be  solid  or  liquid,  or  may  become  molten  during  the 
operation.  They  may  accordingly  be  divided  into  three  classes  : — 

(1)  Furnaces  with  solid  resisting  contents.    The  material  to 
be  heated  in  these  furnaces  is  sufficiently  conducting  to  serve  as  a 
resistor,  and  remains  solid  during    the  operation  of    the  furnace. 
Such  furnaces  are  in  consequence  usually  intermittent  in  action, 
the  charge  being  heated  and  allowed  to  cool  before  it  can  be  re- 
moved from  the  furnace. 

The  Acheson  graphite  furnaces,  for  the  manufacture  of 
graphite  from  anthracite  coal,  Fig.  38,  p.  145,  and  for  graphitic- 
ing  carbon  electrodes,  Fig.  39,  p.  145,  are  the  most  important 
members  of  this  class.  The  material  of  the  charge  is  a  sufficiently 
good  electrical  conductor  to  permit  the  current  to  pass  without 
needing  any  special  conducting  core,  and  the  resulting  graphite, 
being  quite  infusible,  remains  in  position  in  the  furnace,  which 
must  therefore  be  allowed  to  cool  before  the  charge  can  be  re- 
moved. Other  examples  are  the  Cowles  zinc  furnace,  Fig.  42, 
p,  157,  the  Johnson  zinc  furnace,  Fig.  43,  p.  158,  and  the  Thom- 
son electric  welding  apparatus. 

(2)  Furnaces  with  melting  resisting  contents.      The    great 
majority   of   electric   smelting   furnaces   are   in   this  class.         The 
current  passes   between   electrodes    through   the  contents  of    the 
furnace,   and  these  contents   melt  and  run   down  in   the  furnace. 
Such  furnaces   are  almost  invariably  continuous   in   action,   fresh 
material  being  supplied  at  intervals,  and  the  molten  products  being 
tapped  off  while  the  furnace  is  running.        Almost  all  materials, 
when  in  a  melting  condition,  are  sufficiently  conducting  to  carry 
the  current,  although  they  may  scarcely  conduct  at  all  when  cold. 

In  these  furnaces  the  current  may  pass  between  a  pair  of 
lateral  electrodes  as  in  Fig.  16,  or  it  may  pass  from  one  or  more 

The    figure    does    not    show    the    arrangement    very   clearly.      The    blocks    are    laid 
across   each   other   so   as    to   form    a  hollow   square  tower  with  openings   in   the    sides. 


CLASSIFICATION.  2~ 

movable  electrodes  to  a  fixed  electrode  forming  part  of  the  bottom 
of  the  furnace  as  in  Fig.  17.  The  furnace  illustrated  in  Fig.  16, 
consists  of  a  chamber  provided  with  lateral  carbon  electrodes  and 
one  or  more  tapping  holes.  It  has  a  striking  resemblance  to  a 
blast  furnace,  the  electrodes  representing  the  tuyeres.  The  ore 
becomes  heated  and  reduced  to  the  metallic  state  in  the  upper 


Fig.  16. — Shaft  Furnace  with  Lateral  Electrodes. 

part  of  the  furnace,  and  the  whole  charge  melts  in  the  zone  be- 
tween the  electrodas,  and  can  be  tapped  out  at  the  bottom.  The 
current  passes  in  part  through  the  molten  slag  and  metal  in  the 
bottom  of  the  furnace,  as  well  as  directly  through  the  melting  ore 
between  the  two  electrodes.  An  objection  to  this  type  of  furnace  is 
that  the  current  cannot  be  effectively  regulated  by  moving  the 
electrodes. 

The  Harmet  furnace,  Fig.  31,  p.  114,  is  an  example  of  this 
class. 

Fig.  17  represents  a  furnace  with  one  large  electrode  hung  in 
the  middle,  surrounded  by  the  material  to  be  heated.  The  other 
electrode,  B,  is  fixed,  forming  part  of  the  bottom  of  the  furnace ; 
and  merely  serves  to  make  electrical  contact  with  the  fused  ma- 
terial in  the  furnace.  An  advantage  in  this  furnace  is  that  the 
current  can  be  easily  regulated  by  raising  or  lowering  the  upper 
electrode.  Moreover,  the  hottest  part  of  the  charge  is  in  the 
middle  of  the  furnace,  thus  leading  to  a  greater  economy  of  heat 
and  to  a  longer  life  of  the  furnace  walls. 


28 


THE     ELECTRIC     FURNACE. 


The  Heroult  ore  smelting  furnace,  Fig.  29,  p.  108;  the 
Haanel-Heroult  furnace,  Fig.  32,  p.  116,  and  the  Salgues  zinc 
furnace,  Fig.  45,  p.  160,  are  in  this  class. 


Fig.   17.— Shaft  Furnace  with  Central  Electrode. 

(4)  Furnaces  with  liquid  resisting  contents.  These  consist  of 
a  refractory  reservoir,  containing  fused  slag,  or  metal,  through 
which  the  electric  current  passes.  The  liquid  becomes  super- 
heated by  the  passage  of  the  current,  and  is  able  to  melt  the  fresh 
material,  which  can  be  added  at  intervals  or  continuously.  The 
current  is  introduced  by  carbon  electrodes,  by  water-cooled  metal 
electrodes,  or  by  induction. 

The  De  Laval  furnace,  Fig.  18,  is  in  this  class;  it  consists  of 
a  chamber,  A,  the  lower  part  of  which  is  divided  into  two  troughs, 
B  and  C,  containing  molten  metal,  with  which  electrical  contact  is 
made  by  metal  terminals.  A  molten  slag,  E,  fills  the  furnace 


OF 
'FC 


CLASSIFICATION. 


above  the  dividing  wall,  and  the  electric  current  flows  between  B 
and  C  through  the  molten  slag.  The  slag  becomes  superheated 
and  dissolves  the  ore,  F,  which  is  added  through  a  hole,  K,  in 
the  top  of  the  furnace.  Alternating  current  should  be  employed 
to  avoid  electrolysis.  The  slags  fills  the  furnace  up  to  the  hole, 
F,  at  which  it  overflows.  The  metal  in  the  troughs  overflows  at 
the  spouts,  G  and  H,  as  fast  as  it  is  formed.  In  order  to  prevent 
the  current  melting  away  the  wall  between  the  troughs  a  water- 
cooled  metal  bl«ck,  J,  is  inserted.  Even  with  this  precaution 


Fig.  18.— De  Laval  Ore=smelting  Furnace. 

there  is  danger  of  short-circuiting,  because  the  metal  in  B  and  C 
may  penetrate  to  the  water  jacket,  J,  thus  forming  a  complete 
metallic  connection  between  the  furnace  terminals. 

The  Snyder  induction  smelting  furnace,  Fig.  47,  p.  166,  re- 
sembles the  Laval  furnace,  but  the  electric  current  is  generated  in 
the  Snyder  furnace  by  induction,  instead  of  being  led  in  by  metal 
terminals  or  electrodes. 

Furnaces  having  resistors  of  liquid  metal  are  used  in  electric 
steel  making.  Such  furnaces  consist  of  a  long  canal  containing 
the  molten  steel  which  becomes  heated  by  the  passage  of  the 


30  THE     ELEC1RIC     FURNACE. 

electric  current.  The  canal  is  usually  folded  backwards  and 
forwards  for  compactness,  and  to  reduce  the  loss  of  heat.  The 
current  may  be  led  in  through  water-cooled  metal  terminals,  as  in 
the  Gin  furnace,  Fig.  28,  p.  104;  but  it  is  preferably  generated 
directly  in  the  molten  metal  by  induction,  the  canal  forming  the 
short-circuited  secondary  winding  of  a  transformer,  as  in  the 
Kjellin  steel  furnace,  Fig.  24,  p.  93  ;  the  Gronwall  steel  furnace, 
Fig.  26,  p.  100,  and  the  Colby  steel  furnace,  Fig.  25,  p.  97,  and 
Frontispiece. 

III. — Electrolytic  Furnaces. 

In  these  furnaces  the  power  of  a  continuous  current  to  divide 
a  fused  chemical  compound  into  two  component  parts  is  utilized, 
while  the  heating  effect  of  the  current  is  also  needed  to  keep  the 
contents  of  the  furnace  in  a  state  of  fusion.  Most  chemical  com- 
pounds can  be  decomposed  in  this  way,  but  some  behave  like  the 
metals  and  alloys,  and  carry  the  current  without  suffering  de- 
composition. Mixtures  of  two  or  more  compounds  are  often 
employed,  as  this  facilitates  the  passage  of  the  current  and 
renders  the  charge  more  fusible. 


Fig.    19. — Electrolytic  Furnace. 

Fig.  19,  represents  a  furnace  for  the  electrolysis  of  fused  zinc 
chloride,  it  consists  of  a  chamber,  A,  containing  the  fused  chloride, 
B.  The  positive  electrode,  C,  is  made  of  carbon,  and  dips  into 


CLASSIFICATION.  31 

the  electrolyte,  while  the  fused  zinc,  D,  resulting  from  the  opera- 
tion, forms  the  negative  electrode;  electrical  connection  being 
made  with  it  at  E.  The  passage  of  the  current  splits  the  zinc 
chloride  into  zinc,  which  collects  at  D,  and  chlorine,  which  is 
liberated  at  the  electrode,  C,  and  is  withdrawn  from  the  furnace 
by  the  pipe,  F.  A  cylinder,  G,  passes  through  the  roof  of  the 
furnace  and  dips  into  the  fused  electrolyte,  to  enable  fresh  chloride 
to  be  added  without  allowing  the  chlorine  to  escape. 

Furnaces  for  the  production  of  aluminium  (Figs.  5  and 
52)  are  also  electrolytic. 

The  classification  adopted  in  this  chapter  is  shown 
diagramatically  on  the  next  page ;  an  example  of  each  type  being 
S"iven. 


THE     ELECTRIC     FURNACE. 


CO 

0> 
O 

^ 

^ 
a 

S_i 

o 

rt 

furnace). 
:  ore  smelting 

'  CD 

1 

5-1 

cu 

r_( 

p 

. 

,_^ 

on 

a 
fa 

CD 
O 
rt 

a 

5-H 

iS 

en 

"a 

o3 

CO 

on 

Siemens'  vertica 

"oT 

O 

CJ 

a 

in 

CD 
,£3 
3 

-4-1 

13 

o 

rundum  furnace) 

^     3 

0  ^ 

£H 
^     '^ 

^  2 

c^  S 

"  r— 

CD 

'^ 
J 

^ 

% 

G 

V-i 

^ 

s 

'o 

O 

a 

o 
13 

1 

.2   c 

rnace 

inium 

< 

bJD 

^c/T 

CD 

'c5     0 

<5 

g 

a 

.5 

.—i 

v- 

Cd    ^ 

,  ,  _, 

3 

0 

c 

rt 

3 

_G 

^"  •  T~~ 

p^ 

'tj 

'& 

CD 

^ 

O 

on 

o 

^\ 

^H 

r^ 

p 

^_) 

CO 

•  1-^ 

^) 

CD 

-4—  ' 

•  i—  1 

3 

>t 

"t* 

5S 

& 

2 

_0 

o 

0     ' 

0 

3 

"co 

a 

3 

en 

-4-J 

on 

> 

O 

"o 

—4 

^  ,, 

-  -> 

'on 

'on 

J^> 

Q^ 

CD 

^2 

!' 

CD 

CD 

f 

VI 

r-^1 

en 
cu 

% 

F?  *  'rf  2 


Si'g 


1  5 

ci 


EFFICIENCY    AND    COST.  33 

CHAPTER  III. 

EFFICIENCY   OF    ELECTRIC   AND    OTHER    FURNACES, 

AND  RELATIVE  COST  OF  ELECTRICAL  AND 

FUEL  HEAT. 

Electricity  would  generally  be  preferable  to  fuel  for  producing 
heat,  if  it  were  not  that  the  cost  of  electrical  energy  is  almost  in- 
variably greater,  and  usually  many  times  greater  than  that  of  an 
equivalent  amount  of  fuel.  In  certain  operations,  such  as  the 
production  of  carborundum  or  graphite,  electricity  must  be  em- 
ployed, because  a  sufficiently  high  temperature  cannot  be  obtained 
by  the  combustion  of  fuel.  In  other  operations,  such  as  the  pro- 
duction of  aluminium,  the  electrolytic  action  of  the  electric  cur- 
rent is  essential  to  the  process.  A  large  number  of  metallurgical 
operations,  however,  were  carried  on  successfully  .before  electric 
smelting  was  thought  of ;  and  for  such  purposes  electricity  is  only 
employed  when  its  greater  efficiency  and  convenience  out-weigh 
the  usually  greater  cost.  It  has  recently  been  realized  that 
electricity  can  sometimes  economically  replace  coal  or  coke  as  a 
heating  agent  in  operations  such  as  the  smelting  of  zinc  or  even 
lion  ores,  or  in  the  production  of  steel. 

In  comparing  electricity  and  coal,  we  may  consider  how  much 
heat  each  will  produce,  or  how  much  electrical  energy  will  be 
needed  to  produce  as  much  heat  as  one  pound  of  coal  would  yield 
on  burning.  One  unit  or  kilowatt  hour  of  electrical  energy  will 
produce  3,415  B.  T.  U.  (British  Thermal  Units),  of  heat,  and  one 
pound  of  good  quality  coal  will  produce  about  14,000  B.  T.  U. 
Thus  four  kilowatt  hours  are  needed  to  produce  as  much  heat  as 
one  pound  of  coal. 

For  small  consumers,  buying  electrical  energy  for  lighting  at 
10  or  15  cents  a  unit,  and  coal  at  $6  or  $7  a  ton,  the  cost  of 
electrical  heat  would  be  one  or  two  hundred  times  that  of  coal  heat. 

As  a  year  consists  of  8,766  hours,  one  kilowatt  would  yield,  if 
operated  continuously  for  that  time,  nearly  30,000,000  B.  T.  U., 
or  one  electrical  H.P.  year  would  yield  22,320,000  B.  T.  U.  ;  and 
as  one  ton  of  coal  will  produce  about  31,000,000  B.  T.  U.,  it  will 
be  seen  that  an  electrical  H.P.  year  produces  about  25  per  cent, 
less  heat  than  a  ton  of  good  coal ;  or  one  ton  of  coal  would  pro- 
duce as  much  heat  as  i^  E.  H.  P.  years.  If  an  electrical  H.P. 
year  could  be  purchased  for  $30  and  a  ton  of  coal  for  $4,  the  cost 
of  electrical  heat,  per  B.  T.  U.  would  be  ten  times  the  cost  of  coal 
heat. 


34  THE     ELECTRIC     FURNACE. 

In  localities  where  water-power  can  be  cheaply  developed,  and 
where  transportation  charges  for  coal  and  coke  are  high,  it  may  be 
possible  to  produce  electrical  power  at  $10  or  less  per  E.  H.  P. 
year,  in  large  amounts  as  would  be  necessary  for  electric  furnace 
work,*  and  coal  may  cost  $6  or  $8,  w7hile  furnace  coke  might  cost 
even  more  than  that.  Under  such  conditions  the  cost  of  electrical 
heat  would  be  less  than  twice  that  of  coal  heat,  and  would  ap- 
proximate to  the  cost  of  heat  furnished  by  good  furnace  coke. 

It  might  appear  from  these  figures,  that  electrical  heating 
could  not  be  profitably  employed,  except  under  the  most  extreme 
conditions  of  cheap  power  and  dear  fuel,  but  it  should  be  re- 
membered that  in  an  electric  furnace,  a  large  proportion  of  the 
heat  supplied  is  actually  utilized  in  heating  the  materials  in  the 
furnace,  while  in  a  coal-fired  furnace  this  is  not  always  the  case, 
and  often,  particularly  in  high  temperature  furnaces,  the  greater 
part  of  the  heat  is  wasted,  and  only  a  small  proportion  is  actually 
utilized. 

The  efficiency  of  a  furnace  may  be  determined  by  finding  wrhat 
proportion  of  the  heat  value  of  the  coal  or  the  electrical  energy 
supplied,  is  actually  utilized  in  heating  the  contents  of  the  furnace. 
The  following  tablet  gives  typical  efficiencies  for  a  number  of 
furnaces. 


TABLE  II. 
Net  Efficiencies  of  Furnaces  used  for  Melting  Metals. 

Per  Cent. 

Crucible  steel  furnaces,  fired  with  coke     2-3 

Reverberatory  furnaces  for  melting  metals       Io-I5 

Regenerative  open-hearth  steel  furnaces       20-30 

Shaft  furnaces  (foundry  cupolas,  etc.) 30-50 

Large  electrical  furnaces  60-8  s 


*Prof.  C.  E.  Lucke,  (Electrochemical  Industry,  vol.  v.,  p.  230,  June,  1907),  gives 
the  cost  of  water-power  as  $8.50  to  $25  per  K.W.  year.  Dr.  R.  S.  Hutton,  (Electro- 
chemical Industry,  vol.  v.,  p.  24,  January,  1907),  gives  figures  for  cheap  water-power, 
varying  from  $20  per  H.P.  year  at  Niagara,  to  $3  per  H.P.  year  in  Norway.  Dr. 
Haanel,  (European  Report,  1904,  p.  32),  says  he  is  "credibly  informed  that  the  water-, 
power  at  Chats  Falls  can  be  developed  at  a  cost  to  produce  an  E.H.P.  year  at  the 
rate  of  $4.50." 

fThe  figures  are  taken  from  Prof.  J.  W.  Richards'  "Metallurgical  Calculations," 
Part,  i,  p.  89. 


EFFICIENCY    AND    COST. 


35 


These  efficiencies  relate  to  the  melting  of  metals,  but  similar 
figures  would  be  obtained  for  the  same  furnaces  employed  in  smelt- 
ing ores.  In  the  crucible  steel  furnace  and  the  reveberatory 
furnace,  the  greater  part  of  the  heat  is  carried  away  in  the  escap- 
ing gases,  which  are  necessarily  extremely  hot ;  and  in  the  crucible 
furnace  the  loss  is  additionally  high  on  account  of  the  slow  trans- 
mission of  the  heat  to  the  steel  inside  the  crucible.  In  the  open- 
hearth  furnace,  the  loss  of  heat  due  to  the  escaping  gases  is  very 
much  less  because  the  heat  they  contain  is  given  to  the  brick- 
work in  the  regenerators  or  checker  chambers,  and  returned  from 
these  to  the  furnace  by  the  incoming  gas  and  air.  In  shaft 
furnaces  the  heat  of  the  furnace  gases  is  largely  absorbed  by  the 
solid  materials  in  the  upper  part  of  the  furnace,  and  by  them  re- 
turned to  the  zone  of  fusion.  When  metals  are  melted  in  the 
electric  furnace,  no  gases  need  be  produced,  and  thus  a  large 
waste  of  heat  is  entirely  avoided ;  while  the  furnace  gases  pro- 
duced in  the  electric  smelting  of  ores  are  very  much  less  in  amount 
than  those  from  similar  coal  or  gas-fired  furnaces.  The  amount  of 
air  that  passes  through  most  furnaces,  in  excess  of  that  required 
to  burn  the  fuel,  increases  the  loss  of  heat  by  the  furnace  gases ; 
and  the  incomplete  combustion  of  the  fuel  is  another  serious  source 
of  loss  in  some  furnaces.  The  large  loss  of  heat  by  conduction 
and  radiation  from  the  furnace,  is  common  to  fuel  and  electric 
furnaces,  and  depends  mainly  upon  the  size  and  temperature  of 
the  furnace ;  the  larger  furnaces  having,  of  course,  a  smaller 
relative  loss. 


Fig.  20.— Losses  of  Heat  in  Melting  Metals. 

Fig.  20  has  been  arranged  to  show,  for  each  class  of  furnace, 
the  heat  equivalent  of  fuel  or  electrical  energy  needed  to  impart 
unit  quantity  of  heat  to  the  metal  to  be  melted.  The  black  areas 


36  THE     ELECTRIC     FURNACE. 

indicate  the  loss  of  heat,  the  upper  edge  of  each  area  showing  the 
minimum,  and  the  lower  edge,  the  maximum  loss  for  each  class 
of  furnace.  The  diagram  also  shows  that  for  one  heat  equivalent 
supplied  to  an  electric  furnace ;  a  shaft  furnace  would  require 
nearly  two ;  an  open-hearth  furnace  three ;  a  reverberatory  furnace 
six ;  and  a  crucible  steel  furnace  thirty  heat  equivalents  of  fuel,  in 
order  to  melt  the  same  amount  of  metal. 

If  these  numbers  are  used  to  multiply  the  cost  of  a  ton  of  the 
coal  or  coke  used,  assuming  it  to  be  of  about  14,000  B.T.U.,  the 
resulting  prices  may  be  compared  with  the  cost  of  i^i  E.  H.  P. 
years,  and  will  give  an  idea  whether  coal  or  electrical  heating 
would  be  cheaper  in  any  particular  case.  Thus  in  making 
crucible  steel  with  furnace  coke  at  $5  and  the  E.  H.  P.  year  at 
$30,  the  coke  used  would  cost  $5x30  =  $150,  and  the  electrical 
energy  would  cost  $30X1  -^  =  $40,  thus  making  a  good  case  for 
the  electrical  production  of  crucible  steel.  In  the  case  of  the  open- 
hearth  furnace,  electrical  energy  at  $10  an  E.H.P.  year  would 
cost  a  little  more  than  coal  at  $4  a  ton,  while  it  would  correspond 
with  coke  at  $6  to  $7  a  ton  in  a  shaft  furnace.* 

These  numbers  are  based  on  the  mean  of  the  figures  given 
by  Prof.  Richards  for  the  usual  efficiencies  of  certain  classes  of 
furnaces  ;  and  in  any  selected  case  it  would  be  desirable  to  have 
the  efficiencies  of  the  particular  electrical  and  fuel  furnaces  to  be 
compared.  The  incidental  expenses  connected  with  each  method 
of  smelting  should  also  be  considered. 

The  results  do,  nevertheless,  give  a  fair  idea  of  the  conditions 
under  which  electrical  heat  could  commercially  replace  fuel  heat. 
They  show  clearly,  that  in  the  production  of  crucible  steel, 
electrical  power  should  be  able  to  replace  coke  as  a  source  of  heat. 
The  writer  pointed  out,  more  than  three  years  years  ago,t  that  the 
production  of  crucible  steel  in  the  electric  furnace  was  technically 
and  financially  possible,  and  plants  are  now  in  operation  or  con- 
struction in  Sweden,  Germany,  England,  the  United  States,  Can- 
ada, and  elsewhere. 

In  comparing  the  cost  of  electrical  and  fuel  heating,  it  has 
been  assumed  that  the  full  heat  value  was  obtained  from  the 
electrical  horse-power  year.  To  obtain  this,  it  would  be  neces- 
sary for  the  furnaces  to  be  operated  at  their  full  load  for  every 


*See    also    editorial    "Electric    Heat    versus    Heat    from    Fuel,"    Electrochemical    In- 
dustry,   vol.    v.,    p.    298. 

•f-Stansfield,  The   Electrothermic   Production   of  Iron   and  Steel,   Trans.   Can.    Soc.    of 
Civil    Engineers,   vol.    xviii.,    Part    i,    (19^;),    p.    72. 


EFFICIENCY    AXD    COST.  37 

minute  of  the  year,  and  any  shut-down,  or  any  period  during 
which  a  smaller  amount  of  power  was  being  utilized,  would  lessen 
the  useful  effect,  without  any  corresponding  reduction  in  the 
amount  paid  for  the  power ;  as  it  is  bought  by  the  year,  and  not 
by  the  total  kilowatt-hours  consumed.  In  the  case  of  fuel-fired 
furnaces,  a  shut-down,  or  a  period  of  reduced  output,  will  increase 
the  working  cost  per  ton  of  product;  but  not  to  the  same  extent, 
as  the  fuel  is  usually  bought  by  the  ton,  and  not  on  some  assumed 
standard  of  maximum  consumption.  The  time  during  which  a 
single  electric  furnace  is  shut  down  for  repairs  will  necessarily  in- 
crease decidedly  the  working  cost  of  electrical  energy ;  but  when 
electric  smelting  has  become  well  established,  the  losses  in  this 
way  will  not  be  heavy.  In  the  regular  operation  of  an  electric 
smelting  plant,  there  will  be  fewr  accidental  shut-downs,  all  work- 
ing furnaces  will  be  kept  at  a  steady  load,  and,  by  means  of  spare 
furnaces,  the  full  load  will  be  maintained  during  the  periodical 
lay-off  of  each  furnace  for  repairs. 

Having  now  considered,  in  a  general  manner,  the  efficiency 
of  furnaces  and  the  relative  costs  of  electrical  and  fuel  heating, 
the  method  of  calculating  these  efficiencies  may  be  discussed. 

The  Calculation  of  Furnace  Efficiencies.* 

The  word  heat  is  used  popularly  in  two  senses;  thus  "the 
beat  of  a  furnace,"  meaning  how  hot  the  furnace  is,  is  quite  dis- 
tinct from  the  amount  of  heat  produced  in  the  furnace  per  minute, 
or  the  amount  of  heat  needed  to  turn  a  pound  of  ice  into  a  pound 
of  water.  The  first  use  is  really  a  quality  of  the  hot  body,  and  to 
avoid  confusion  the  word  temperature  should  be  used  in  such 
cases,  while  the  word  heat  should  be  restricted  to  the  second  case, 
in  which  the  quantity  of  heat  is  referred  to.  A  definite  quantity 
of  heat  can  be  supplied  at  a  high  or  a  low  temperature,  just  as  a 
definite  quantity  of  air  can  be  supplied  at  a  high  or  a  low  pressure ; 
and  the  addition  of  heat  to  a  body  raises  the  temperature,  just  in 
the  same  way  that  pumping  air  into  a  receiver  raises  the  pressure. 

Temperatures  are  measured,  as  is  well  known,  by  ther- 
mometers or  pyrometers  (the  latter  for  high  temperatures),  and 
the  scales  of  these  instruments  are  based  upon  the  temperatures 
of  melting  ice  and  boiling  water,  these  being  o°  and  100°  on  the 
Centigrade  scale,  and  32°  and  212°  on  the  Fahrenheit  scale.  The 
use  of  these  two  scales  complicates  technical  literature,  since  the 

*For   a  full  account,  with   examples,   of  the   calculation   of  furnace   efficiencies,    see 
Prof.   J.  W.  Richards'  "Metallurgical  Calculations,"  Parts   I.,  II.,  and  III. 


38  THE     ELECTRIC     EURXACE. 

Centigrade  is  mainly  used  for  scientific  purposes,  while  the  Fahren- 
heit is  mainly  used  for  ordinary  affairs,  and  it  is  often  necessary 
to  state  temperatures  on  both  scales  in  order  to  be  generally  under- 
stood. The  conversion  from  one  scale  to  the  other  is  simple  if 
it  is  remembered  that  the  temperatures  o°C.  and  ioo°C.  are  the 
same  as  32°F.  and  2i2°F.,  and  that  5°  difference  of  temperature 
on  the  Centigrade  scale  correspond  to  9°  difference  of  temperature 
on  the  Fahrenheit  scale;  whence  F.°—  i.8C°  +  32  ;  and  C.°  =  5/9 


Heat  is  measured  in  several  different  units,  thus  further  com- 
plicating technical  writings,  most  of  these  units  representing  the 
amount  of  heat  needed  to  raise  the  temperature  of  unit  weight  of 
water  through  i°.  By  selecting  different  weights  of  water,  as  the 
pound,  gram,  or  kilogram,  and  different  temperature  scales,  it  is 
easy  to  get  six  or  eight  different  units  of  heat,  thus  entailing  a 
large  amount  of  trouble,  both  in  the  statement  of  amounts  of  heat 
and  in  changing  these  from  one  system  of  units  to  another. 

The  following  heat  units  are  usually  used  :— 

The  Gram=calorie.  —  (i  cal.)  —  The  amount  of  heat  needed  to  raise 

the  temperature  of   one  gram   of   wyater   i°C.    (from   o°C.    to 

i°C.)* 
The  Kilogram=Calorie.  —  (i  Cal.)  —  The  amount  of  heat  needed  to 

raise  the  temperature  of  one  kilogram  of  water  i°C. 
The    Pound=Calorie.  —  (i    Calb.)  —  The  amount  of   heat   needed   to 

raise  the  temperature  of  one  pound  of  water  i°C. 
The   British  Thermal  Unit.—  (i   B.   T.    U.)—  The  amount  of  heat 

needed  to  raise  the  temperature  of  one  pound  of  water  i°F. 

(from  6o°F.  to  6i°F.)* 
The  £\7aporative  Unit.  —  The  amount  of  heat  needed  to  convert 

one  pound  of  water  at  2i2°F.  into  steam  at  the  same  tempera- 

ture  (at  normal  atmospheric  pressure). 

The  value  of  the  gram  calorie  depends  upon  the  specific  heat  of  water  between  O°C. 
and  i°C,  and  that  of  the  B.T.U.  on  its  specific  heat  between  6o°F.  and  6i°F.  Recent  de- 
terminations, (II.  T.  Barnes.  The  mechanical  equivalent  of  heat  measured  by  electrical 
means,  Int.  Elect.  Congress,  St.  Louis,  1904,  p.  65),  show  that  the  specific  heat  at 
O°C.  is  about  i  per  cent,  greater  than  at  6o°F.  This  would  mean  that  in  converting 
pound  calories  into  B.T.  Units  by  the  factor  9/5  an  error  of  about  i  per  cent,  would 
be  made.  Also  as  the  measurement  of  heat  is  usually  conducted  between  is°C  and 
2c°C..  a  considerable  correction  will  have  to  he  made  to  reduce  the  results  to  calories 
as  measured  at  O°C.  For  these  and  other  reasons  it  has  been  suggested  that  the 
calorie  should  be  based  on  the  mean  specific  heat  of  water  from  O°C.  to  ioo°C.  This 
value  is  practically  the  same  as  if  measured  at  is°C.,  or  at  6o°F.  The  mechanical 
equivalent  of  one  gram  calorie  of  heat  measured  at  i5°C.  is  about  4.184  joules,  mak- 
ing the  heat  value  of  i  kilowatt  second,  0.2.39  Cals.,  or  0.527  Calb. 


EFFICIENCY    AND    COST.  39 

The  following  are  the  relations  between  these  different  units : 

i  Kilogram-Calorie*  =  1,000  Gram-calories. 

i  Pound-Calorie  =453.6  Gram-calories. 

i  British  Thermal   Unit  =  5/9  of  a  Pound-Calorie. 

i  "  =252  Gram-calories. 

i  Evaporative  Unit  =967  British  Thermal  Units. 

The  gram  and  kilogram-calories  are  the  most  convenient  for 
scientific  investigations,  but  in  cases  where  the  weights  are  given 
in  pounds  the  pound-calorie  or  the  B.T.U.  must  usually  be  em- 
ployed. 

The  efficiency  of  a  furnace  is  the  ratio  between  the  amount  of 
heat  usefully  employed  in  the  furnace  and  the  heat  value  of  the 
fuel  or  electrical  energy  supplied :  thus,  if  100  pounds  of  steel  can 
be  melted  in  a  crucible  furnace  by  the  use  of  150  pounds  of  coke, 
and  if  300  pound-calories  are  needed  to  melt  one  pound  of  steel 
(this  having  been  determined  by  experiment),  and  if  one  pound 
uf  coke  can  furnish  7,200  pound-calories  (found  by  experiment), 
the  efficiency  of  the  furnace  can -at  once  be  obtained. 

Weight  of  steel  x  heat  needed  to  melt   i   Ib.   steel. 

Efficiency  = 

Weight  of    coke  x  heat   furnished   by     i    Ib.     coke. 

100  Ibs.  x  300  Calb. 

Efficiency  =  =0.028  =2.8% 

150  Ibs.  x  7,200  Calb. 

The  statement  that  300  pound-calories  are  needed  to  melt 
one  pound  of  steel,  means,  that  if  to  one  pound  of  cold  steel  there 
could  be  added  300  pound-calories  of  heat,  without  any  of  the 
heat  being  lost,  the  steel  would  be  heated  to  its  melting  point  and 
melted.  It  is,  of  course,  impossible  to  do  this,  but  by  pouring 


*In  order  to  distinguish  between  the  kilogram  calorie  and  the  gram  calorie  it  is 
usual  to  use  a  C  for  the  first,  and  a  c  for  the  second,  thus  100  kilogram  calories 
would  be  written  100  Cal.,  and  100  gram  calories  would  be  100  cal.  Prof.  Richards 
suggests  (private  communication)  that  the  same  rule  should  be  followed  with  pound 
calories  and  ounce  calories  (if  such  should  ever  be  needed).  These  would  be  written 
100  Ib.  Cal.  and  100  oz.  cal.  As  long  as  the  Ib.  or  oz.  is  specified  the  large  or  small 
c  are  only  useful  for  analogy,  and  the  Ib.  could  not  be  omitted  without  confusion  with 
kilo  Cal.  The  author  suggests  the  contraction  Calb.,  for  pound-calories. 


40  THE     ELECTRIC     FURNACE. 

some  molten  steel  into  a  vessel  of  water,  and  noting  the  rise  of 
temperature  of  the  water,  the  number  of  calories  given  out  by  the 
steel  in  cooling  can  be  determined,  and  this  is  obviously  the  same 
as  the  amount  of  heat  needed  to  melt  the  steel.  The  number  of 
calories  being  equal  to  the  product  of  the  weight  of  water  and  its 
rise  of  temperature,  corrections  being  made  for  the  heat  ab- 
sorbed by  the  vessel  and  otherwise  lost  during  the  experi- 
ment. 

The  amount  of  heat  needed  to  melt  one  pound  of  each  of  the 
common  metals,  and  the  temperature  at  which  they  melt,  are  given 
in  the  following  table ;  the  figures  have  all  been  obtained  by  ex- 
periment, with  the  exception  of  the  heat  of  fusion  of  wrought  iron, 
which  has  been  calculated  : — 


TABLE  III. 

Melting  Temperatures  of  Metals,  and  Amounts  of  Heat  Required 

to  Melt  Them. 

Metal.  Melting  Temperature      Heat  to  melt  i  Ib. 

C.*  F.  Calb.t  B.T.U. 

Tin      232°                450°  28  51 

Lead     327°               620°  16  28 

Zinc      419°                786°  68  122 

Aluminium         657°               1214°  258  465 

Brass  (65%  copper) 920°              1688°  130  234 

Copper     1084°              1983°  162  292 

Cast  iron  J  (white) 1027°- 1 135°   i88o°-2o75° 

(gray) noo°-i275°  201 2° -232*7°  245  441 

Tool  steel  (i%  carbon).  ..    1425°              2600°  300  540 
Wrought    iron    or   "dead 

soft"  steel     1503°             2737°  343  617 

The   figures   in   the  last   two    columns  really    represent     the 
amount  of  heat  given  out  by  one  pound  of  the  metal  in  cooling 

"Melting  temperatures  of  pure  metals  as  given  by  Dr.  J.  A.  Marker.  The  figure 
for  copper,  i,o84°C.,  is  its  melting  temperature  when  protected  from  oxidation,  by  a 
cover  of  charcoal  for  example.  Oxidized  copper  melts  at  i,o62°C. 

fThese    figures    are   mainly   from    Richards'    "Metallurgical  Calculations." 
+  Melting    temperatures    of   Cast    Iron    were   determined    by    Prof.    H.    M.    Howe,    see 
his    Metallurgical   Laboratory   Notes,    p.    125. 


EFFICIENCY    AND    COST.  41 

from  the  molten  state  to  32°F.  In  heating  the  metal  from  60°  or 
7o°F.  rather  less  heat  will  be  needed,  but  on  the  other  hand,  some 
additional  heat  will  be  required  in  order  that  the  metal  shall  be 
thoroughly  melted,  and  the  heat  actually  needed  to  heat  the  metal 
to  a  casting  temperature  will  be  a  little  more  than  the  figures  in 
the  table. 

The  amount  of  heat  that  can  be  produced  from  one  pound  of 
coke,  can  be  determined  by  burning  a  small  weighed  quantity  of 
the  coke  in  a  calorimeter ;  which  is  an  instrument  for  measuring 
the  amount  of  heat  that  is  produced.  The  amount  of  heat  pro- 
duced by  unit  weight  of  a  fuel,  is  known  as  its  calorific  power,  and 
is  usually  measured  in  the  corresponding  heat  units ;  that  is,  heat 
units  containing  the  same  unit  of  weight ;  as,  for  example,  the 
number  of  gram  calories  produced  by  one  gram  of  fuel ;  the  number 
of  pound  calories  produced  by  one  pound  of  fuel,  or  the  number  of 
B.T.U.  produced  by  one  pound  of  fuel.  The  first  two  of  these 
results  will  obviously  be  identical,  and  may  be  called  the  Centi- 
grade calorific  power,  while  the  last  result  will  be  9/5  times  as 
large,  and  may  be  called  the  Fahrenheit  calorific  power.  Thus 
the  calorific  power  of  carbon  is  8,100  on  the  Centigrade  scale,  .tnu 
14,580  on  the  Fahrenheit  scale,  meaning  that  one  part  by  weight 
of  carbon  would  give  out  as  much  heat,  if  completely  burnt,  as 
would  raise  the  temperature  of  8,100  parts  of  water  i°C.,  or  14,- 
580  parts  of  water  i°F.,  so  the  result  is  the  same,  whatever  unit 
of  weight  is  selected.  When,  however,  the  fuel  is-  measured  by 
volume,  as  in  the  case  of  a  gas,  it  will  be  necessary  to  state  the 
calorific  power  as  so  many  B.T.U.  per  cubic  foot,  or  calories  per 
cubic  foot,  or  per  cubic  meter.  Calorific  powers  are  also  some- 
times stated  in  evaporative  units,  thus  avoiding  the  use  of  either 
scale  of  temperature. 

In  many  furnaces  the  carbon  in  the  fuel  is  not  burnt  completely, 
and  it  then  has  a  smaller  effective  calorific  power.  The  com- 
plete combustion  of  carbon  produces  the  gas  CO2,  containing  two 
atoms  of  oxygen,  while  its  incomplete  combustion  produces  the 
gas  CO,  containing  only  one  atom  of  oxygen.  The  calorific 
power  in  the  latter  case  being  only  2,43oC.,  or  4,374F.,  which  is 
less  than  one-third  of  its  calorific  power  when  burnt  completely. 
The  iron  blast-furnace  furnishes  a  good  example  of  this  loss  of 
heat  through  the  imperfect  combustion  of  the  coke.  In  order  to 
thoroughly  reduce  the  iron  ore  to  metal  a  large  amount  of  coke 
must  be  present  in  the  furnace,  and  this  can  only  be  burnt  to  CO 
in  the  lower  part  of  the  furnace,  thus  obtaining  far  less  heat  from 
the  same  weight  of  coke  than  if  it  could  be  burnt  completely  to 


42  THE     ELECTRIC     FURNACE. 

CO2.  The  CO  produced  in  the  lower  part  of  the  furnace  is,  how- 
ever, partly  utilized,  higher  up,  for  the  reduction  of  the  iron  ore, 
and  the  CO  that  finally  escapes  from  the  furnace  is 
employed  as  a  fuel  for  heating  the  blast  and  for  raising- 
steam. 

In  determining  the  calorific  power  of  a  fuel  in  a  calorimeter, 
the  aqueous  vapor  resulting  from  the  burning  of  any  hydrogen  in 
the  fuel,  and  any  moisture  and  "combined  water"  in  the  fuel,  will 
be  condensed  to  water ;  and  its  latent  heat  of  condensation  will  be 
included  in  the  resulting  calorific  power.  When  the  fuel  is  burnt 
in  any  metallurgical  furnace,  the  furnace  gases  escape  at  too  high 
n  temperature  to  allow  of  the  condensation  of  the  vapor,  and  in 
calculating  furnace  efficiencies  a  calorific  power  should  be  used 
which  does  not  include  the  heat  of  condensation  of  the  water 
vapour,  since  this  heat  can  never  be  obtained  in  the  furnace.  The 
observed  calorific  power  should,  therefore,  be  corrected  by  sub- 
stracting  from  it  the  heat  of  condensation  of  all  the  water  vapor 
that  is  present  in  the  fuel,  or  is  produced  by  its  combustion.  The 
corrected  value  has  been  called  the  Metallurgical  or  Practical 
Calorific  Power, *  and  should  be  used  in  the  case  of  all  furnaces 
from  which  the  water,  contained  in  the  furnace  gases,  escapes  in 
the  form  of  vapour. 

The  following  table  contains  the  Metallurgical  Calorific 
Powers  of  some  of  the  commoner  fuels,  and  some  pure  substances. 
The  calorific  powers  of  fuels  cannot,  however,  be  stated  exactly, 
as  they  vary  considerably. 

The  figures  in  this  table  are,  in  many  cases  lower  than  the 
calorific  powers  obtained  experimentally  in  a  calorimeter,  the  dif- 
ference being  the  correction  of  606.5  pound-calories  per  pound  of 
water  in  the  products  of  combustion  ;  this  amount  of  heat  being- 
needed  to  evaporate  a  pound  of  water  at  O°C.  In  calculating 
furnace  efficiencies  by  means  of  this  table,  the  furnace  will  thus 
be  debited  with  the  sensible  heat  carried  by  the  water  vapour  as 
well  as  with  that  carried  by  the  other  furnace  gases,  but  the  heat 
of  condensation  of  the  water  vapour  will  have  been  removed  from 
the  balance  sheet. 


'Prof.    J.   W.   Richards'   loc.   cit. 


EFFICIENCY    AND    COST. 


43 


TABLE  IV. 


Calorific  Powers. 


(All  water  remaining  uncondensed.) 

C.  F. 

Calb.*  B.T.U.t 


Carbon  (burnt  to  CO2),  per  Ib.  8,100  14,580 

|  "       H     CO     "     "  2,430  4,374 

Carbon  monoxide      ....    "  2,43O  4^374 

Carbon  monoxide.  .  .per  cu.  ft.  191  344 

Hydrogen       per  Ib.  29,030  52,254 

per  cu.  ft.  163  293.5 
Methane  (Marsh  gas, 

CH4.)                      "     "     "  537  966 
Ethylene  (Olefiant  gas, 

C2H4).  904  1,627 

Wood  (air  dried), per  Ib.  about  3,000  about  5,400 

Peat        "                               "      "  3,000-  4,000  5,400-  7,200 
Charcoal  (  5  to  10  per  cent. 

moisture)        per  Ib.  7,000-  7,500  12,500-13,500 

Oven  coke 6,900-  7,400  12,400-13,300 

Anthracite       "     "  6,500-7,500  11,500-13,500 

Bituminous  coal       7,000-  8,000  12,500-14,500 

Fuel  oil      "      "  9,500-11,000  17,000-20,000 

Natural  gas      per  cu.  ft.  460-      540  830-      970 

Coal  gas   "      "      "  300-      360  550-      650 

Water  gas      ......      "      "      "  140-       180  250-      320 

Producer  gas      ....      "      "      "  55-        90  TOO-       160 

Electrical  energy,  per  kilowatt 

hourj      1,897  3,4J5 

Electrical  energy,    per   E.H.P. 

hour      Ti4I5  2,547 

Electrical  energy,    per   E.H.P. 

year  of  8,766  hours   ....  12,400,000  22,320,000 

*The  values  for  pure  substances  in  this  column  are  those  adopted  by  Pro/. 
Richards. 

•f-These  values  are  obtained  by  multiplying  the  figures  in  the  previous  column 
by  the  factor  9/5. 

+The  values  for  electrical  energy  have  been  calculated  in  terms  of  the  specific 
heat  of  water  at  i5°C.,  i  kilowatt-second  being  0.239  Cal.,  or  0.527  Calb. 


44  THE     ELECTRIC     FURNACE. 

The  calorific  powers  of  the  pure  substances,  forming  the  first 
part  of  the  table,  will  serve  as  data  for  calculating  the  calorific 
power  of  a  gaseous  fuel  of  known  composition,  and  will  enable 
approximate  figures  to  be  obtained  for  solid  and  liquid  fuels.  The 
coal  and  other  solid  fuels  in  the  lower  part  of  the  table  are  sup- 
posed to  be  in  the  condition  in  which  they  would  naturally  occur : 
the  wood  being  air  dried,  and  containing  some  20  to  25  per  cent, 
of  moisture,  the  peat  also  air  dried  and  retaining  20  to  30  per  cent, 
of  moisture;  the  charcoal,  coke  and  coal  have  the  usual  amounts 
of  ash  and  moisture.  The  figures  given  for  coal  and  other  fuels 
will  not  cover  all  cases,  but  are  intended  to  represent  the  ordinary 
run  of  fuels.  The  calorific  powrers  of  gases,  per  cubic  foot, 
correspond  to  dry  gas  at  32°F.,  and  would  be  about  5  per  cent, 
less  at  6o°F.,  and  7  per  cent,  less  at  7o°F.  on  account  of  the  in- 
crease in  volume  of  the  gas  :  the  presence  of  moisture  would  still 
further  decrease  the  calorific  power. 

By  the  aid  of  Tables  III.  and  IV.  it  will  be  easy  to  obtain, 
approximately,  the  percentage  efficiency  of  any  furnace,  whether 
fired  by  solid,  liquid,  or  gaseous  fuel,  or  heated  electrically — if  it 
is  employed  for  heating  and  melting  metals,  and  if  the  amount  of 
fuel  or  electrical  energy  corresponding  to  the  melting  of  a  certain 
weight  of  metal  is  known.  It  will  not  be  possible,  however,  to 
calculate  in  the  same  manner  the  efficiency  of  a  furnace,  such  as 
an  open-hearth  steel  furnace,  in  which  the  metal  is  kept  molten 
for  some  hours  in  order  to  allow  of  certain  changes  being  made 
in  its  composition.  In  such  a  furnace  the  efficiency  can  only  be 
calculated  in  reference  to  the  time  during  which  the  charge  was 
being  heated.  During  the  remainder  of  the  "heat"  the  furnace 
may  remain  for  considerable  periods  without  any  marked  rise  of 
temperature,  although  fuel  is  constantly  being  used ;  thus  making 
the  calculated  efficiency  zero  during  such  periods. 

I  he  efficiencies  of  metal-melting  furnaces  were  first  considered 
on  account  of  the  simplicity  of  the  calculation.  But  it  is  equally 
possible  to  calculate  the  efficiency  of  a  blast  furnace,  or  an 
electrical  ore-smelting  furnace,  in  which  the  heat  is  used,  not 
merely  in  melting  a  metal,  but  also  in  effecting  the  chemical  work 
of  reducing  the  ore  to  a  metallic  condition.  The  amounts  of  heat 
necessary  for  the  formation  of  a  large  number  of  chemical  com- 
pounds are  known,  and  by  means  of  these,  it  is  possible  to  draw 
up  a  balance  sheet  showing  what  amount  of  heat  is  needed  for  the 
chemical  reactions,  as  well  as  for  melting  the  metal  and  slag  in  the 
furnace.  The  efficiency  can  then  be  calculated  as  in  the  simpler 
cases. 

It  may  be  of  interest,  and  practical  value,  to  conclude  this 
chapter  by  calculating  the  efficiency  of  a  Heroult  electrical  steel 


EFFICIENCY    AND    COST.  45 

furnace,  operated  at  La  Praz,  France,  for  the  Haanel  commission 

in  March,  1904.*    The  furnace — basic  lined,  was  making  steel  by 

melting  scrap  with  ore  and  lime. 

The  charge  selected  for  calculation   (number  660)   consisted 

of:— 

Lbs. 

Steel  scrap        5>733 

Iron  ore     43° 

Lime       346 

Other  additions  were  made  after  the  charge  was  melted,  but 
for  obtaining  the  melting  efficiency  it  will  only  be  necessary  to  con- 
sider the  operation  of  melting  this  charge  in  the  furnace. 

The  scrap  charged  had  the  following  composition : — 

Carbon     o.  1 1  o 

Silicon       o.  1 52 

Sulphur 0.055 

Phosphorus       0.220 

Manganese      o.  130 

Arsenic 0.089 

Supposing  that  the  iron  ore  in  the  charge  contained  400 
pounds  of  ferric  oxide,  it  may  be  assumed,  that  during  the  melt- 
ing of  the  charge,  this  was  reduced  to  ferrous  oxide  by  the  oxida- 
tion of  most  of  the  metalloids  and  some  of  the  iron  in  the  original 
scrap.  A  rough  calculation  shows  that  the  melted  charge  would 
consist  of  about  5,660  pounds  of  "dead  soft"  steel,  and  850  pounds 
of  slag  rich  in  ferrous  oxide  and  lime,  and  that  the  reaction  would 
produce  some  24,000  pound-calories,  which  makes  a  small  addi- 
tion to  the  heat  furnished  by  the  electric  current. 

Assuming  that  a  temperature  of  i,52o°C.  is  necessary  for  n 
complete  fusion  of  the  charge  (see  Table  III.),  about  344  Calb.  will 
be  needed  to  melt  each  pound  of  soft  steel,  or,  in  all,  344  x  5,660 
—  1,947,000  Calb. 

The  slag  will  need  about  600  Calb.  per  pound  in  order  to  melt 
and  heat  it  to  the  same  temperature,  or,  in  all,  600  x  850=510,000 
Calb. 

The  electrical  power  employed  was  215  kilowatts  during  the 
first  hour,  and  342  during  the  remainder  of  the  run ;  the  current 
being  supplied  at  about  no  volts.  The  time  occupied  in  melting 


'Report  of  the  Commission  appointed  to  investigate  the  different  electro-thermic 
processes  for  the  smelting  of  iron  ores  and  the  making  of  steel  in  Europe,  pp.  54, 
55,  71  and  72. 


46  THE     ELECTRIC     FURNACE. 

the  charge  was  5^/3  hours,  and  the  electrical  energy  supplied  to  the 
furnace  during  this  time  was  1,680  kilowatt  hours. 

The  heat  supplied  by  the  electric  current  was  : — 

i, 680  x  1,897-3,187,000  Calb.      (See  Table  IV.). 

In  the  operation  of  melting  the  charge  the  heat  utilized  may 
be  taken  as  that  needed  to  melt  the  steel  and  the  slag,  while  the 
heat  supplied  to  the  furnace  is  supplied  in  part  by  the  electric  cur- 
rent, and  in  part  by  the  reaction  between  the  scrap  and  the  iron 
ore. 

Balance  Sheet  of  Heat. 

Heat  supplied  to  the  furnace  :  Calb. 

i, 680  kilowatt  hours  of  electrical  energy    3,187,000 

Reaction  between  steel  scrap  and  iron  ore 24,000 


Total 3 , 2 1 1 ,000 

Heat  utilized  in  the  furnace  : — 

To  melt  5,660  Ibs.  of  soft  steel     . .  . .  .  .  1,947,000 

To  melt  850  Ibs.  of  basic  slag 510,000 


Total 2,457,000 


2,457,000 
Efficiency  of  furnace  =  =0.765  =  76.5%. 

3,21 1,000 

In  making  this  calculation  it  has  been  assumed  that  no  oxida- 
tion of  the  steel  scrap  took  place  except  by  reaction  with  the  iron 
ore  in  the  charge.  Such  an  assumption  would  be  quite  wrong  in 
regard  to  an  open-hearth  furnace,  where  the  flame  of  burning 
gases  constantly  plays  over  the  charge,  but  in  the  electric  furnace 
the  charge  is  largely  protected  from  the  air,  and  there  is  conse- 
quently less  oxidation.  If  any  considerable  amount  of  iron  were 
burnt  in  this  way,  the  heat  produced  by  its  oxidation  should  have 
been  added,  in  the  balance  sheet,  to  the  heat  supplied  to  the 
furnace  ;  and  this  would  lower  the  resulting  figure  for  the  efficiency. 
After  the  charge  was  completely  melted,  the  slag  was  poured 
off,  and  the  steel  further  purified  by  the  addition  of  fresh  slags, 
made  of  lime,  sand  and  fluor  spar.  After  these  were  removed, 
the  steel  was  recarburized  in  the  furnace  by  additions  of  "car- 
burite"  (a  mixture  of  iron  and  carbon)  and  ferro-silicon  ;  some 
ferro-manganesc  was  also  added,  and  a  little  aluminium  in  the 
ladle. 


EFFICIENCY    AND    COST.  47 

The  yield  of  ingots  was  5,161  Ibs.  of  tool  steel  of  the  fol- 
lowing composition  : — 

Carbon       , 1.016 

Silicon      o.  103 

Sulphur      0.020 

Phosphorus     0.009 

Manganese      o.  1 50 

Arsenic     0.060 

Three  hours  were  required  for  the  purification  and  carburiza- 
tion  of  the  steel,  making  a  total  of  8y$  hours,  and  a  total  consump- 
tion of  2,580  kilowatt  hours,  or  0.171  E.H.P.  years  per  ton  of 
steel  ingots.  At  $10  per  E.H.P.  year,  the  cost  of  electrical 
energy  for  the  ton  (2,240  Ibs.)  of  tool  steel  would  be  $1.71. 


48 


THE     ELECTRIC     FURNACE. 


CHAPTER   IV. 


Electric  Furnace  Design,  Construction  and  Operation. 

An  electric  furnace  consists  essentially  of  some  substance  R, 
(Fig.  21),  through  which  an  electric  current  flows,  and  of  an 
envelope  C,  which  retains  the  heat  and  the  contents  of  the  furnace. 
Carbon  electrodes,  A  and  B,  are  usually  needed  to  convey  the  cur- 
rent in  and  out  of  the  furnace.  If  the  envelope  could  be  made 
perfectly  heat  tight,  and  if  no  fresh  charge  were  introduced  dur- 
ing the  operation,  it  would  be  possible  to  obtain  any  temperature 
in  R  up  to  the  volatilizing  point  of  the  contents  of  the  furnace, 


Fig.  21. — Ideal  Electric  Furnace. 

with  the  smallest  electric  current,  provided  it  were  allowed  to  pass 
for  a  sufficient  length  of  time.  With  the  materials  actually  avail- 
able for  furnace  construction  this  is  not  possible.  For  a  definite 
size  and  construction  of  furnace,  a  definite  rate  of  heat  production 
will  be  needed  in  order  to  attain  any  particular  temperature. 

The  rate  of  production  of  heat  is  measured  by  the  number  of 
Watts  of  electrical  power  supplied  to  the  furnace,  and  may  con- 
veniently be  stated  in  Watts  per  cubic  inch,  or  Kilowatts  per  cubic 
foot  of  the  interior  volume  of  the  furnace.  The  rate  of  heat 
production  which  is  necessary  to  enable  a  certain  temperature  to 
be  attained,  may  be  calculated  from  a  consideration  of  the  area, 
thickness  and  conductivity  for  heat  of  the  walls  of  the  furnace ; 
but  it  is  more  easily  obtained  by  reference  to  furnaces  of  similar 
construction  which  have  attained  definite  temperatures  with 
definite  consumption  of  electric  power. 

The  above  considerations  apply  more  particularly  to  an  inter- 
mittent furnace  such  as  the  Moissan,  or  Stassano  furnaces,  in 
which  a  charge  of  ore  or  metal  is  submitted  to  the  heat  of  the 
electric  current  until  it  has  all  been  reduced  or  melted,  and  the 


CONSTRUCTION    AND    DESIGN.  49 

whole  of  the  furnace  and  its  contents  has  been  heated  to  a  uni- 
form high  temperature.  In  the  case  of  a  continuous  furnace, 
such  as  the  Heroult  furnace  recently  employed  to  smelt  iron  ores 
at  Sault  Ste.  Marie,  Fig.  29,  p.  108,  a  constant  stream  of  cold 
material  enters  the  furnace,  and  after  reduction  and  fusion,  is 
tapped  out  as  molten  pig  and  slag ;  only  a  portion  of  the  contents 
of  the  furnace  being  heated  at  any  one  time  to  the  smelting 
temperature.  In  such  a  furnace  the  temperature  attainable  is 
limited  by  the  melting  temperature  of  the  charge ;  any  increase 
in  the  rate  of  heat  supply  will  serve  mainly  to  increase  the  rate  of 
smelting,  without  materially  increasing  the  temperature  of  the 
furnace.  It  is  like  melting  ice  in  a  pail,  the  ice  melts  faster  on  a 
hot  day  than  on  a  cool  one,  but  the  water  surrounding  the  ice  will 
not  become  warm  as  long  as  there  is  any  ice  left  to  melt.  Even 
in  such  a  furnace  each  portion  of  the  charge  must  ultimately  be 
heated  to  the  smelting  temperature,  and  a  definite  rate  of  heat 
supply  is  needed  if  the  furnace  is  to  smelt  at  all. 

Materials  of  Furnace  Construction. 

The  materials  for  constructing  the  interior  of  electric  and 
other  furnaces,  should  be  infusible  at  the  temperature  of  the 
furnace ;  should  resist  the  action  of  the  metallic  slags  or  other 
contents  of  the  furnace ;  should  retain  the  heat  of  the  furnace  as 
far  as  possible,  and  should  be  capable  of  being  formed  into  bricks, 
or  coherent  linings  which  will  resist  the  mechanical  action  of  the 
charge  in  the  furnace.  The  following  are  a  number  of  the  more 
important  materials  that  can  be  employed. 

Fireclay  Bricks.*  The  clay  from  which  these  are  made  con- 
sists of  pure  clay,  or  kaolin,  AbO3,  2SiO2,  2H2O,  with  a  variable 
proportion  of  silica  in  addition  to  the  amount  present  in  the  kaolin, 
and  as  little  as  possible  of  fluxing  materials  such  as  iron  oxide, 
lime,  magnesia,  potash  or  soda.  Even  silica  lowers  the  melting 
point,  and  should  be  present  only  in  moderate  amount.  These 
bricks  are  largely  used  for  lining  ordinary  metallurgical  furnaces, 
but  are  not  usually  sufficiently  refractory  for  electric  furnaces  ;  they 


*Notes  on  the  New  Jersey  Fire-Brick  Industry,  H.  Ries.  Amer.  Inst.  Mining 
Engineers,  vol.  xxxiv.,  (1904),  p.  254. 

Refractoriness  of  Some  American  Fire-Brick.  R.  F.  Weber,  Amer.  Inst.  Mining 
Engineers,  vol.  xxxv.,  p.  637. 

The  Fire-Clays  of  Missouri.  II.  A.  Wheeler,  Amer.  Inst.  Mining  Engineers,  vol. 
xxxv.,  p.  720. 

Determination  of  the  Refractoriness  of  Fire-Clays.  H.  O.  Hofman  &  C.  D.  Demond, 
Amer.  Inst.  Mining  Engineers,  vol.  xxiv.,  p.  42;  vol.  xxv.,  p.  3;  vol.  xxviii.,  p.  435. 

A.  H.  Sexton,  "Fuel  and  Refractory  Materials,"  (textbook). 


50  THE    ELECTRIC     FURNACE. 

can,  however,  be  used  as  a  backing  for  more  refractory  material. 
Being  silicious  in  composition,  they  are  easily  fluxed  by  slags  con- 
taining metallic  oxides.  When  not  exposed  to  such  slags  they 
will  stand  temperatures  up  to  i,4OO°C. — i,8oo°C.,  or  2,5oo°F. — 
3,3oo°F.  They  should  be  laid  in  fireclay  mud,  instead  of  lime 
mortar,  as  the  latter  would  crumble  away  if  strongly  heated. 
Fireclay  bricks  are  subject  to  a  considerable  shrinkage  when  fired. 
This  shrinkage  is  permanent  and  varies  in  amount  with  the 
temperature  to  which  the  bricks  have  been  heated.  Subsequent 
heating  and  cooling,  at  lower  temperatures,  causes  a  small 
temporary  expansion  and  contraction  of  the  brick. 

Silica  Bricks.*  These  should  contain  about  95%  to  97%  of 
silica,  SiO2.  The  melting  temperature  of  silica  is  a  little  above 
that  of  platinum,  being  about  i,83O°C.,  or  3,33o°F.,t  and  the 
silica  brick  should  stand  up  to  about  i,75o°C.,  or  3,i8o°F.  They 
are  useful  for  the  roof  and  other  parts  of  open-hearth  steel 
furnaces,  that  are  exposed  to  a  very  high  temperature,  but  not 
subjected  to  the  action  of  metallic  slags  which  would  soon  flux 
them  away.  They  have  the  property  of  expanding  when  fired, 
and  their  expansion  and  contraction  when  subsequently  heated 
and  cooled  is  greater  than  that  of  fireclay  bricks.  Silica  bricks 
should  be  laid  in  a  silicious  mud  for  mortar,  and  in  general,  all  re- 
fractory bricks  should  be  laid  in  mortar  of  the  same  composition 
as  the  brick,  to  avoid  fluxing ;  thus  it  would  not  do  to  lay  basic 
brick  in  silicious  mortar,  as  the  mortar  would  combine  with  and 
flux  part  of  the  brick. 

Lime,  CaO.t  This  is  an  extremely  refractory  material,  and  is 
useful  for  lining  small  electric  furnaces.  Its  melting  temperature 
is  not  exactly  known,  but  may  be  about  2,o5o°C. ,  or  3,7oo°F.§ 
Lime  is  obtained  by  burning  limestone,  (CaO,  CO2),  thus  driving 
off  the  carbon  dioxide  which  it  contains.  Burnt  lime  absorbs 
moisture  from  the  air  and  slakes,  forming  the  hydroxide  CaO, 
H2O.  Lime  mortar  contains  water  and  carbon  dioxide,  and 


*A.    H.    Sexton.      "Fuel    and    Refractory  Materials,"    p.    323. 

•f-O.  Boudouard,  finds   the  melting  temperature  of  pure  silica  to   be   i,83o°C.     Journ. 
Iron   &    Steel    Inst.,   vol.   1905,    No.    I.,   p.   350. 

A.    Lampen,    finds    the    melting    temperature   ot    pure    quartz   to   be    i,7oo°C.      Journ. 
Amer.  Chem.   Soc.,  vol.  xxviii.,  p.  852. 

A.    Stansfield    found    pure    silica    to    be     rather    less    fusible    than     platinum,    say, 
i,8oo°C.,   (determination   about   1892,    unpublished). 

+  A.   H.    Sexton.     "Fuel   and   Refractory  Materials,"    p.    317. 
II.    Moissan,    "The    Electric    Furnace." 

§O.    Boudouard,   loc.    cit.   apparently   assumes    the    melting   temperature    of   lime    to 
be   about  2,o5o°C. 


CONSTRUCTION    AND    DESIGN.  51 

when  it  is  heated  in  a  furnace,  these  are  driven 
off,  and  the  mortar  crumbles  away.  Lime  cannot  be  made  into 
fire  bricks  by  mixing  it  with  water,  as  the  bricks  would  crumble 
in  the  furnace,  and  it  is  difficult  to  render  lime  coherent  by  the  use 
of  any  other  material.  This  difficulty  of  binding  and  liability  to 
slake  has  prevented  the  general  use  of  lime  for  furnace  linings. 
Small  electric  and  oxy-hydrogen  furnaces  may  be  constructed  of 
blocks  of  quick-lime  or  of  the  natural  limestone  which  becomes 
converted  internally  into  lime  during  the  operation  of  the  furnace. 
Being  basic  or  non-silicious  in  character,  lime  will  resist  the  action 
of  metallic  slags,  and  it  would  form  a  valuable  material  for  lining 
electric  and  other  furnaces  if  it  were  not  for  the  objections  already 
mentioned.  The  use  of  lime  in  the  electric  furnace  is  also  limited 
by  its  property  of  forming  a  fusible  carbide  when  heated  with 
carbon. 

Magnesia.*  Burnt  Magnesite,  Magnesite  Bricks,  MgO. 
Magnesia  is  even  more  refractory  than  lime,  melting  at  perhaps 
2,ioo°C.,  or  3,8oo°F.  It  is  produced  by  burning  magnesite  (MgO, 
CO2),  thus  driving  off  the  carbon  dioxide,  in  the  same  way  that 
lime  is  produced  from  limestone.  Although  it  resembles  lime 
chemically,  magnesia  does  not  slake  very  easily,  and  when  strongly 
burned  it  shrinks  considerably,  forming  a  heavy  material  very  dif- 
ferent from  the  light,  chemically  prepared  magnesia  which  is  used 
as  a  medicine.  The  shrunk  magnesia  can  be  cemented  together 
to  form  a  moderately  strong  fire-brick,  which  is  extremely  valuable 
for  lining  basic  open-hearth  furnaces  and  electric  furnaces. t  It 
is  not  easily  fluxed  by  metallic  slags,  since  it  is  basic  in  composi- 
tion. On  account  of  their  great  compactness  (a  brick  weighs 
about  8T2  Ibs.),  they  are  very  good  conductors  of  heat,  being 
about  twice  as  good  as  fire-clay  bricks,  and  in  constructing  electric 
furnaces  of  magnesite  bricks  an  outer  coating  of  some  other  ma- 
terial should  be  used  to  diminish  the  loss  of  heat,  except  when  this 
cooling  is  desired  to  prevent  the  fluxing  of  the  walls.  Magnesite 
bricks  are  liable  to  crack  under  the  influence  of  heat  unless  it  is 
gradually  applied.  Their  property  of  contracting  when  heated 
renders  them  unsuitable  for  building  the  arched  roofs  of  furnaces, 
and  silica  bricks  would  be  used  for  this  purpose  except  in  furnaces 
where  the  roof  was  exposed  to  a  temperature  at  which  they  would 
melt.  Furnace  linings  may  also  be  constructed  of  burnt  magnesite 
in  the  form  of  a  powder ;  it  is  mixed  with  tar  or  pitch  to  make  it 


*A.   H.   Sexton.   "Fuel   and   Refractory  Materials,"   p.   335. 

•f-A.  Lampen,  loc.  cit.   gives  the  melting  temperature  of  fused  magnesia  as  2,ooo°C., 
and   that   of  magnesia   brick    with   high   percentage   iron   as    i,9oo°C.    to  a,ooo°C. 


52  THE     ELECTRIC     FURNACE. 

bind,  and  rammed  into  place  around  a  core  by  means  of  a  hot  iron 
rod.  Magnesia  does  not  combine  with  carbon  to  form  a  carbide, 
and  on  this  account  its  use  in  the  electric  furnace  is  preferable  to 
that  of  lime.  Electrically  fused  magnesia  has  recently  been 
obtained,  and  forms  a  very  compact  and  refractory  material  for 
lining  electric  furnaces,  or  it  may  be  applied  as  a  paste  mixed  with 
silicate  of  soda  to  render  ordinary  fire-clay  bricks  more  re- 
fractory.* 

Dolomite.  This  is  a  limestone  containing  a  considerable  pro- 
portion of  magnesite,  and  when  burnt  it  forms  a  valuable  refrac- 
tory material,  which,  like  burnt  magnesite,  may  be  employed  as 
e  powder,  or  in  the  form  of  bricks.  It  resembles  magnesite,  but 
is  not  Quite  so  good. 

In  furnaces  constructed  partly  of  silica  bricks,  and  partly  of 
dolomite,  or  magnesite  bricks,  it  would  be  expected  that  they 
would  flux  one  another  at  the  line  of  contact.  On  this  account, 
a  course  of  chromite  brick  is  sometimes  introduced  as  a  parting 
layer  between  the  two,  as  this  brick,  itself  very  refractory,  does 
not  easily  flux  with  either  acid  (siliceous)  or  basic  materials. 
When  magnesite  bricks  are  used,  however,  it  is  found  that  this 
precaution  is  unnecessary. 

Alumina,  AbC^.t  This  is  prepared  from  the  mineral  bauxite 
(Al2C>3,  2H2O),  which  is  also  the  source  of  the  metal  aluminium. 
Bauxite  has  long  been  used  as  a  lining  for  furnaces  and  recent  at- 
tempts at  purification  with  a  view  to  improving  it  for  use  as  a  re- 
fractory material,  have  been  successful;  and  the  purified,  calcined 
bauxite  bonded  with  a  little  fire  clay,  sodium  silicate,  or  lime,  makes 
an  excellent  brick ;  which  appears  to  be  as  good  as  magnesite  brick 
for  use  in  the  basic  open-hearth  furnace.  It  is  also  said  to  be  a 
good  lining  for  rotary  Portland  cement  kilns,  and  for  lining  lead 
refining  furnaces,  where  they  are  exposed  to  the  fluxing  action 
of  corrosive  lead  slags.  Alumina  is  classed  as  a  basic  material, 
like  magnesia  or  dolomite,  and  its  melting  temperature  is  about 

2,IOO°C.t 

Carbon.  (Coke,  Charcoal,  Graphite).  Carbon  is  the  most 
refractory  substance  known  ;  it  has  never  been  melted,  but  softens 
and  volatilizes  at  the  temperature  of  the  electric  arc,  that  is  about 


*Klectrically-shrunk  magnesia,  see  paper  by  E.  K.  Scott,  quoted  Electrochemical 
Industry,  vol.  iii..  (1905),  p.  140. 

f  A.   H.   Sexton.     "Fuel  and  Refractory   Materials,"  p.   319. 

tj.  W.  Richards,  "Metallurgical  Calculations,"  vol.  i.,  p.  95,  gives  the  melting 
point  of  alumina  as  about  2,2oo°C. 

O.  Boudouard,  loc.  cit.  gives  data  which  point  to  about  2,ioo°C.  as  the  melting 
temperature  of  alumina. 


CONSTRICTION    AND    DESIGN1.  53 

3,700°C.,  or  6,7oo°F.*  In  its  more  compact  forms  it  is  a  fair 
conductor  of  electricity  and  of  heat,  the  former  quality  together 
with  its  infusibility  enabling  it  to  be  used  for  electrodes  to  lead  the 
current  into  electric  furnaces.  Being  combustible  it  is  liable  to 
waste  away  when  exposed  to  the  air  at  a  red  heat,  and  for  the 
same  reason  it  is  corroded  when  exposed  to  slags  that  contain 
easily  reducible  metallic  oxides.  Carbon  exists  in  the  three  dif- 
ferent forms  of  amorphous  carbon,  graphite  and  diamond;  char- 
coal, coke  and  the  other  common  forms  of  carbon  being  of  the 
amorphous  variety.  When  amorphous  carbon,  or  the  diamond 
are  heated  to  the  temperature  of  the  electric  arc,  they  are 
changed  into  graphite.  Carbon  blocks  composed  of  coke  or 
graphite  can  be  used  for  lining  furnaces,  provided  they  are  not 
exposed  to  air  or  to  oxidising  slags,  but  carbon  has  not  been 
much  us^d  for  metallurgical  furnace  linings.  In  the  electric 
furnace  it  is  often  employed,  forming  a  lining  which  also  serves  as 
an  electrode,  as  in  the  Heroult  iron  smelting  furnace,  (Fig.  29, 
p.  108),  the  aluminium  furnace,  (Fig.  5,  p.  7),  and  the  \Yillson 
carbide  furnace,  (Fig.  7,  p.  10) ;  but  it  cannot  usually  be  employed 
for  the  entire  lining,  because  it  is  so  good  a  conductor  of  electricity 
that  the  current  would  tend  to  be  short-circuited  by  the  lining-  in- 
stead of  passing  through  the  charge  or  resistor  in  the  furnace. 
Coke  powder  can  be  used  for  lining  parts  of  furnaces,  using  pitch 
or  tar  as  a  binder,  and  such  linings  will  conduct  the  electric  cur- 
rent and  may  be  used  as  electrodes.  In  experimental  work  a  lin- 
ing of  charcoal  powder  cemented  with  molasses  and  water  may 
sometimes  be  used,  and  has  the  advantage  that  it  retains  the 
heat  of  the  furnace  very  well,  and  being  a  poor  electrical  con- 
ductor, it  can  be  used  for  the  entire  lining  without  fear  of  short- 
circuiting  the  current.  If  exposed  to  the  air,  however,  it  will  burn 
up  completely  if  it  once  reaches  a  red  heat.  Graphite  is  a  better 
conductor  of  electricity  and  of  heat  than  amorphous  carbon,  and  is 
less  easily  oxidised  by  air  or  metallic  slags ;  hence,  electrodes  are 
often  composed  of  it.  Graphite  is  often  used  in  the  construc- 
tion of  crucibles,  the  graphite  being  mixed  with  its  own  weight  of 
fire-clay.  The  graphite  renders  the  fire-clay  refractory,  and  the 


*The  temperature  of  the  positive  carbon  of  the  electric  arc  was  determined  by 
Violle  to  be  3,5oo°C.,  aud  he  modified  this  figure  later  to  3.6oo°C.  (Wright,  Electric 
Furnaces,  p.  9).  Le  Chatelier  obtained  the  figure  4,ioo°C.  by  his  optical  pyrometer 
(Le  Chatelier  &  Boudouard  High  Temperature  Measurements,  p.  155).  Lummer.  by  a 
radiation  method  gives  the  temperature  as  between  3,soo°C.  and  3,9oo°C.  (Le  Chatelier 
&  Boudouard,  p.  212).  Fery  has  obtained  the  values  3,49o°C.,  3,869°C.,  and  3,897^. 
bv  different  optical  methods,  (Wright,  p.  277).  The  value  3,7oo°C.  is  adopted  by 
Richards  (Metallurgical  Calculations,  vol.  i.,  p.  62),  as  the  "boiling  point"  of  carbon. 

5 


54  THE     ELECTRIC     FURNACE. 

fire-clay  protects  the  graphite  from  oxidation.  These  crucibles 
are  not  so  refractory  as  the  graphite  alone  would  be,  and  for 
electric  furnace  experiments,  crucibles  may  be  cut  out  of  a  block 
of  graphite  or  retort  carbon. 

For  lining-  electric  furnaces,  when  carbon  is  undesirable,  some 
products  of  the  electric  furnace  itself  are  very  suitable.  They 
are  not  so  refractory  as  carbon,  but  are  more  refractory  than  the 
other  furnace  materials  such  as  magnesia,  silica,  lime  or  alumina. 

Carborundum.*  This  is  produced  by  heating  silica  and 
carbon  to  a  very  high  temperature  in  the  electric  furnace.  It  is 
a  crystallized  compound  of  silicon  and  carbon  having  the  formula 
SiC,  and  besides  being  valuable  as  an  abrasive,  it  forms  a  very 
refractory  furnace  lining.  The  carborundum  powder  can  be 
made  to  cohere  by  the  use  of  fire-clay  (6  parts  of  the  powder  to 
i  of  fire-clay),  or,  by  a  solution  of  silicate  of  soda,  or  water  glass, 
which  should  be  very  dilute  if  the  highest  temperatures  are  to  be 
reached,  as  the  silicate  of  soda  makes  the  carborundum  less  re- 
fractory. Tar  or  glue  can  also  be  used  as  binding  materials,  and 
a  very  strong  brick  can  be  obtained  by  using  glue  as  a  temporary 
cement  and  exposing  the  moulded  article  to  an  oxidizing  atmos- 
phere at  a  high  temperature  for  some  hours,  when  the  partial  oxi- 
dation of  the  carborundum  furnishes  silica  which  acts  as  a  per- 
manent bond. 

Carborundum  Fire=Sand.  This  is  a  name  applied  to  the  un- 
crystallized  variety  of  carborundum,  which  is  found  in  the  cooler 
parts  of  the  carborundum  furnace.  It  only  differs  from  car- 
borundum in  not  being  crystalized,  and  can  be  used  in  the  same 
manner  as  a  refractory  material. 

Siloxicon.t  This  is  made  in  the  same  manner  as  carborundum, 
but  less  carbon  is  used  in  the  charge,  with  the  result  that  the 
silica  is  not  completely  reduced,  and  the  resulting  substance  re- 
tains some  oxygen.  The  composition  is  not  constant,  as  a  series 
of  compounds  are  formed,  but  a  typical  formula  is  Si2C2O.  This 


"The  Carborundum  Furnace,  F.  A.  J.  FitzGerald,  Electrochemical  Industry,  vol. 
iv.,  (1906),  p.  53. 

The  Electrochemical  Industries  of  Niagara  Falls,  F.  A.  J.  FitzGerald,  Electro- 
chemical Industry,  vol.  iii.,  p.  253. 

Refractory  Materials  in  Electrical  Resistance  Furnaces,  F.  A.  J.  FitzGerald, 
F.lectrochemical  Industry,  vol.  ii.,  (1904),  p.  439. 

Refractory  Materials  for  Furnace  Linings,  E.  K.  Scott,  Electrochemical  Industry, 
vol.  iii.,  (1905),  p.  140. 

•f-Oxidation    of   Siloxicon,   E.    G.    Acheson,    Electrochemical   Industry,    vol.    i.,    p.    373. 

Siloxicon  Brick,  Elctrochemical  Industry,  vol.  i.,  pp.  287  and  373;  vol.  ii.,  p.  442; 
vol.  iii.,  p.  445;  vol.  iv.,  p.  40. 


CONSTRUCTION    AND    DESIGN.  55 

forms  a  refractory  material  for  lining  furnaces,  and  may  be  made 
to  cohere  by  grinding  it  to  powder,  moistening  the  powder 
with  water,  pressing  it  into  a  mould,  and  strongly  firing 
the  moulded  material.  The  firing  probably  oxidizes  the 
siloxicon  grains  superficially,  forming  silica  which  acts  as  a 
bond.  Siloxicon  is  said  to  be  unaffected  by  acid  or  basic  slags, 
and  to  be  undissolved  by  molten  iron,  but  although  this  may  be 
true  at  moderate  furnace  temperatures  it  can  scarcely  hold  at  the 
higher  temperatures  of  the  electric  furnace. 

The  silicon  carbides,  although  very  refractory,  are  slowly 
oxidized  at  high  temperatures  in  the  presence  of  air;  siloxicon 
oxidizing  when  heated  above  i,47o°C.,  or  2,674°F.  Carborundum 
was,  for  a  long  time  thought  to  be  unoxidizable,  but  it  has  been 
found  to  oxidize  slowly  at  high  temperatures. 

These  substances  are  far  less  refractory  than  carbon,  being 
dissociated  into  graphite  and  silicon  vapour  at  high  electric 
furnace  temperatures.*  They  can  be  used  in  some  forms  of 
electric  furnace  as  a  layer  protecting  some  less  refractory  material 
such  as  fire-clay  or  magnesite  bricks,  and  applied  as  a  paint  mixed 
with  silicate  of  soda  they  improve  very  materially  the  lasting 
qualities  of  fire-clay  bricks  in  ordinary  metallurgical  furnaces. 

TABLE  V. 
Refractory  Materials. 

Material.  Melting  Temperature. 

/  i,4oo°C.  2,55o°F. 
Fire-clay  brick.  Kaolin  with  additional  silica  J  to  to 

I  i,8oo°C.       3,27o°F. 

(i,7oo°C.  3>ioo°F. 
Silica  brick.  Silica  with  binding  material ..  -  to  to 

(i,8oo°C.  3,27o°F. 

Silica  (pure)  i,83o°C.  3,33Q°F. 

Lime  (pure)  about  2,o4o°C.  3,7oo°F. 

Magnesia  brick  "  2,ooo°C.  3,6oo°F. 

Bauxite  brick  "  2,ooo°C.  3,6oo°F. 

Magnesia  (pure)  "  2,ioo°C.  3,8oo°F. 

Alumina  (pure)  "  2,ioo°C.  3,8oo°F. 

Carborundum,  SiC decomposes  2,22o°C.  4,ooo°F. 

Carbon  boils  3,7oo°C.  6,7oo°F. 


*S.   A.  Tucker  and  A.   Lampen,  Amer.   Chem.   Soc.,  vol.   xxviii.,  p.    858,  find   the  dis- 
sociation temperature  of  carborundum  to  be  a,22o°C.* 


56  THE     ELECTRIC     FURNACE. 

Note. — Very  little  reliable  information  with  reg'ard  to  the  melting 
temperatures  of  refractory  materials  is  available  and  the  above  table 
must  be  regarded  as  an  attempt  to  combine  what  little  there  is,  in 
the  hope  that  experimenters  may  be  induced  to  supply  the  missing  in- 
formation. With  regard  to  silica,  the  writer,  a  number  of  years  ago, 
found  the  chemically  pure  material  to  be  a  little  more  refractory  than 
platinum,  say  i,8oo°C.,  while  Bouclouarcl  has  recently  stated  it  to  be 
i,83o°C.  The  data  for  alumina,  lime  and  magnesia  are  very  confus- 
ing ;  Moissan  states  that  alumina  is  more  fusible  than  lime,  and 
magnesia  less  fusible  than  lime,  but  other  figures  g'iven  for  their 
melting  points  give  magnesia  as  2,ooo°C.,  and  alumina  as  about 
2,2oo°C.,  thus  completely  reversing  the  order.  The  figures  stated  in 
the  table  are  based  upon  the  conflicting  information  available.  It 
should  be  remembered,  however,  that  the  melting  points  of  some  of 
these  refractory  materials,  and  still  more  the  dissociating'  points  of 
the  silicon  carbides  may  not  be  sharply  defined  like  the  melting  points 
of  pure  metals,  but  have,  in  the  former  case,  a  range  of  increasing 
softness  before  true  melting  occurs,  and  that  this  melting  temperature 
is  largely  affected  by  the  oxidizing  or  reducing-  atmosphere  in  the 
furnace.  Siloxicon  has  been  said  to  turn  into  carborundum  at  5,ooo°F.J 
or  2,76o°C.,  corborundum  fire-sand  to  crystallize  into  carborundum  at 
7,ooo°F.,  or  3,87o°C.,  and  carborundum  to  be  infusible  at  the  same 
temperature,  while  it  is  admitted  that  these  substances  are  less  re- 
fractory than  carbon,  whose  boiling  point  is  taken  to  be  3,7oo°C.,  or 
6,7oo°F.  Recent  experiments,  however,  place  the  formation  tempera- 
ture of  carbide  of  silicon  at  i,6oo°C.,  its  crystallization  at  i,Q5o°C., 
and  its  decomposition  into  graphite  and  silicon  vapor  at  2,220°.* 


In  addition  to  its  ability  to  resist  high  temperatures  and  cor- 
rosive slags,  the  power  of  a  furnace  lining  to  retain  the  heat  which 
is  produced  in  the  furnace  must  be  considered.  It  is  rare  that 
good  refractory  and  heat  retaining  qualities  are  combined  in  the 
same  material,  and  to  get  the  best  effect  it  is  usually  necessary 
to  adopt  a  stratified  construction,  placing  refractory  materials  on 
the  inside,  and  heat  retaining  materials  outside.  Generally  speak- 
ing the  light  porous  substances  are  good  retainers  of  heat,  while 
heavy  compact  bodies  are  poor  heat  insulators.  Comparatively 
little  information  is  available  with  regard  to  the  conductivity  of 
furnace  materials  for  heat,  particularly  at  high  temperatures.  The 
following  figures  are  taken  from  Prof.  Richards  "Metallurgical 
Calculations,"  (vol.  i,  p.  183)^  to  which  the  reader  is  referred  for 
further  information  : — 


*S.    A.    Tucker    and   A.    Lampen,    loc.    cit. 

fSee    also    a    paper    by   Hutton    and    Beard    on    Heat    Insulation.      Electrical.    Rev., 
N.Y.,   July    aand,    1905,    and    Eng.    Record,    Nov.    25th,    1905. 


CONSTRUCTION    AXD    DESIGN.  57 

TABLE  VI. 

Heat  Conductivities  of  Furnace  Materials. 

In  Centimeter,  Gram,  Second,  Units. 

Fire-clay  bricks     (  o°C. —     5oo°C.)  0.00140 

Fire-clay  bricks (  o°C. — i,3oo°C.)  0.00310 

Alumina  bricks      (  o°C. —    7oo°C.)  0.00204 

Magnesia  bricks       (  o°C. — i,3oo°C.)  0.00620 

Lime     (2o°C.—       98°C.)  0.00029 

Quartz  sand      (i8°C.—       98°C.)  0.00060 

Carborundum  sand    (i8°C.—       98°C.)  0.00050 

Fire  brick  dust     (2O°C.—       98°C.)  0.00028 

Infusorial  earth      (I7°C- —       98°C.)  0.00013 

Infusorial  earth      (  o°C. —    65o°C.)  0.00038 

The  figures  indicate  the  number  of  gram  calories  of  heat 
that  would  pass  in  one  second  through  a  centimeter  cube  of  the 
material,  if  the  hot  and  cold  sides  differed  in  temperature  by  i°C. 
The  best  conductivity  varies  with  the  temperature,  being  greater 
at  high  temperatures,  as  is  shown  by  the  first  two  and  the  last  two 
items  in  the  list.  The  figures  represent  the  mean  conductivity 
for  the  range  of  temperature  indicated,  and  were  probably  obtain- 
ed by  measuring  the  flow  of  heat  through  a  wall  of  definite  thick- 
ness and  area,  the  two  sides  of  which  were  maintained  at  the 
temperatures  mentioned.  It  will  be  understood  that  a  material 
having  a  high  conductivity  for  heat,  as  shown  in  the  table,  Xv^u'd, 
if  used  in  the  construction  of  a  furnace  wall,  allow  a  considerable 
amount  of  heat  to  escape  and  be  wasted.  Light  powders  like 
infusorial  earth  are  good  for  retaining  the  heat  in  a  furnace,  but 
these  do  not  retain  their  heat  insulating  qualities  at  high  tempera- 
tures and  should  only  be  used  as  an  outer  jacket  to  the  furnace. 
Undoubtedly  much  could  be  gained  in  ordinary  furnaces  by  a  more 
careful  attention  to  the  heat  conducting  qualities  of  the  materials 
of  which  the  walls  are  composed,  and  in  electric  furnaces,  where 
the  cost  of  the  heat  is  usually  considerably  greater,  it  is  even  more 
important  to  guard  as  far  as  possible  against  loss.  On  the  other 
hand  cases  are  common  in  large  fuel-fired  furnaces,  and  occur 
even  in  electric  heating,  where  the  importance  of  preserving  some 
portion  of  the  furnace  that  is  exposed  to  corrosive  slags  or  very 
high  temperatures  is  greater  than  the  need  to  save  the  heat,  and 
in  such  cases,  air  cooling,  and  even  water-cooling  of  the  furnace 
walls  may  be  adopted.  It  should  be  remembered  that  the  rate 


58  THE     ELECTRIC     FURNACE. 

of  loss  of  heat  from  a  furnace  will  be  proportional  to  the  area  of 
its  walls,  that  is,  to  the  square  of  the  linear  dimensions.  The 
ratio  of  heat  loss  per  unit  volume  will,  therefore,  be  inversely 
proportional  to  the  dimensions  of  the  furnace,  or  a  furnace  that 
is  .twice  as  large  as  another  (in  linear  dimensions)  will  only  have 
half  as  large  a  heat  loss,  for  a  given  volume  of  the  interior  of  the 
furnace.  This  supposes  the  furnace  walls  to  be  of  equal  thick- 
ness in  the  two  furnaces,  but  in  small  experimental  furnaces  the 
walls  are  usually  thinner  than  they  are  in  full-sized  furnaces,  and 
under  these  conditions  the  small  furnace  fares  even  worse  in  pro- 
portion ;  and  in  the  extreme  case  of  a  small  furnace  constructed 
as  an  exact  model  on  a  scale  of  one  inch  to  the  foot  of  a  large 
furnace,  the  heat  loss  for  each  cubic  inch  of  the  model  would  be 
144  times  as  great  as  from  the  large  furnace,  provided,  of  course, 
that  both  attained  the  same  temperature.  In  other  words  if  the 
furnaces  were  merely  being  kept  hot,  no  work  being  done  in 
them,  the  small  furnace  would  need  144  times  as  much  heat  per 
cubic  inch  as  the  large  furnace  in  order  to  keep  it  heated  to  the 
same  temperature. 

In  Table  VI.  the  figures  in  brackets  show  the  temperatures 
between  which  the  experimental  determinations  were  made,  thus 
in  the  first  line  of  the  table  one  side  of  a  fire  brick  may  have  been 
kept  at  50o°C.  ,  and  the  other  side  at  o°C.  ,  while  the  rate  at  which 
heat  passed  through  it  was  determined.  The  conductivity  in  the 
last  column  is  consequently  a  mean  value  for  the  given 
temperature  range,  and  the  actual  conductivity  of  fire-bricks  at 
high  temperatures  will  be  even  higher  than  the  figure  given  on 
the  second  line.  In  applying  these  figures  to  calculate  the  losses 
of  heat  through  furnace  walls,  it  should  be  remembered  that  the 
heat  transmitted  is  proportional  to  the  cross  section,  that  is,  the 
area  of  the  piece  of  wall  considered,  inversely  proportional  to  its 
thickness,  and  proportional  to  the  difference  of  temperature  be- 
tween the  two  sides  of  the  wall.  The  conditions  are  in  fact  just 
th  same  as  in  the  flow  of  electricity  in  a  conductor.  By  way  of 
comparison  with  the  figures  in  the  table,  it  may  be  mentioned  that 
the  conductivity  for  heat  of  silver  is  i.i,  of  copper  0.9,  and  of  iron 
0.2  when  cold.* 

Furnace  walls  without  refractory  materials.  The  properties 
of  a  number  of  refractory  materials  have  been  considered,  but  it 
not  infrequently  happens,  in  electric  furnace  construction,  that 
the  heat  can  be  developed  in  the  midst  of  a  large  mass  of  the  ma- 
terial to  be  heated  ;  and  although  a  very  high  temperature  may 


Richards'    Metallurgical    Calculations,    vol.    i., 


p.    175. 


CONSTRUCTION    AND    DESIGN.  59 

be  reached  internally,  the  exterior  never  becomes  strongly  heated, 
and  mere  retaining  walls,  which  need  not  be  extremely  refractory, 
can  be  used.  The  best  known  example  of  this  is  the  Acheson 
furnace  for  the  production  of  carborundum  (Fig.  8,  p.  n).  The 
\Yillson  carbide  furnace,  (Fig-.  7,  p.  10),  also  depends  for  its 
preservation  upon  the  unacted  on,  and  relatively  cool  portions  of 
the  charge,  as  the  walls  of  the  crucible  are  only  made  of  iron. 
The  same  principle  can  be  applied  in  the  case  of  continuous  electric 
smelting  furnaces,  by  constructing  the  furnace  in  such  a  way  that 
the  heat  is  developed  within  the  mass  of  ore  descending  in  the 
shaft  of  the  furnace,  and  by  regulating  the  current  so  that  a 
portion  of  the  ore  will  remain  unfused  around  the  sides  of  the 
furnace.  When  this  can  be  done,  no  trouble  will  be  experienced 
in  maintaining  the  walls  for  an  indefinite  period,  even  when  cor- 
rosive slags  are  produced ;  but  this  method  does  not  lend  itself 
readily  to  processes  in  which  the  charge  must  be  heated  consider- 
ably above  its  melting  point,  as  the  hot  central  portion,  being 
liquid,  wTill  mix  with  the  cooler  parts  round  the  sides,  and  will 
eventually  fuse  the  whole  of  the  protecting  layer  of  ore.  The 
device  of  restricting  the  zone  of  highest  temperature  to  the  middle 
of  a  furnace  depends  upon  a  constant  abstraction  of  heat  around 
the  sides.  This  is  usually  the  result  of  the  air-cooling  of  the 
(liter  walls,  but  it  would  be  more  ideal  if  the  cooling  of  the  walls 
could  be  effected  by  a  continual  supply  of  fresh  ore,  so  that  the 
heat  would  not  really  be  wasted,  but  would  be  used  in  heating 
the  fresh  ore.  In  some  cases,  however,  it  is  even  necessary  to 
wiiter-cjol  parts  of  furnaces  in  order  to  preserve  the  walls.  As 
an  example  of  this  may  be  mentioned  the  De  Laval  smelting 
furnace,  (Fig.  18,  p.  29).  This  has  a  dividing  partition  between 
the  two  troughs,  B  and  C,  which  contain  molten  metal  and  serve 
as  electrodes.  The  partition  being  entirely  within  the  furnace, 
will  experience  very  little  air-cooling,  and  the  arrangement  of  the 
electrodes  tends  to  make  the  current  flow  most  strongly  against 
il  in  passing  through  the  slag.  The  partition  will  consequently, 
become  very  hot  at  this  point,  and  would  certainly  dissolve  away, 
if  it  were  not  for  the  cooling  effect  of  the  water-jacket  J  placed 
within  it.  As  further  examples  of  water-cooling,  may  be  men- 
tioned the  water-cooled  electrodes  in  Heroult's  electric  steel 
furnace.  The  electrode  is  cooled,  by  a  water-jacket,  at  the  point 
where  it  passes  through  the  furnace  roof,  and  the  part  exposed 
to  the  air  is  consequently  below  a  red  heat,  and  does  not  oxidize 
as  it  otherwise  would.  With  this  arrangement,  a  closer  joint  is 
maintained  around  the  electrode,  the  roof  is  protected  from  cutting 

] -'«^*?5X 

OF  THE  \ 

NIVER31TY    ] 

V  OF  / 


60  THE     ELECTRIC     FURNACE. 

by  the  flame  issuing  from  the  furnace,  and  less  loss  of  heat  occurs. 
Another  use  of  water-cooling  is  in  electrolytic  furnaces,  when  the 
molten  electrolyte  is  contained  in  an  iron  vessel,  which  is  re- 
quired to  be  gas-tight.  Since  both  the  electrodes  pass  through 
the  \valls  of  the  vessel,  or  the  vessel  itself  may  be  one  electrode, 
it  is  necessary  to  introduce  an  insulating  joint  at  some  point,  and 
this  joint  must  be  unaffected  by  heat,  by  the  electrolyte,  or  by  the 
gases  given  off  in  the  operation.  A  satisfactory  method  of  effect- 
ing this,  is  to  make  the  vessel  in  two  parts,  one  of  which  may 
be  the  lid,  and  to  maintain,  by  water-cooling,  a  layer  of  solidified 
electrolyte  between  the  two  parts,  which  are  slightly  separated. 
This  method  is  employed  in  Borchers'  appliances  for  the 
electrolysis  of  fused  zinc  chloride,  and  for  the  electrolysis  of  fused 
salts  of  lead.*  Electrode  holders  are  sometimes  water-cooled,  to 
prevent  them  from  becoming  unduly  heated,  and  occasionally 
even  the  electrodes  themselves  are  water-cooled,  as  the  metal  tube 
electrode  in  Siemens'  arc  furnace,  (Fig.  3,  p.  5),  or  the  water- 
cooled  iron  electrode  in  Borchers'  aluminium  furnace, t  or  in  Gin's 
steel  furnace,  (Fig.  28,  p.  104). 

Production  of  Heat  in  Electric  Furnaces. 

As  already  mentioned,  the  rate  at  which  heat  is  produced  in 
an  electric  furnace  may  be  measured  by  the  number  of  watts  of 
electrical  power  supplied  to  the  furnace,  allowance  being  made 
when  necessary  for  any  electrolysis  that  takes  place.  A  certain 
rate  of  heating  is  necessary  for  the  attainment  of  a  definite 
temperature;  this  rate  depending  on  the  thickness  and  heat  re- 
taining qualities  of  the  furnace  walls,  upon  the  size  of  the  furnace, 
and  upon  any  cooling  influence,  such  as  the  introduction  of  fresh 
ore  to  the  furnace.  A  few  examples  will  now  be  given  of  the 
rate  of  heat  production  in  typical  electric  furnaces,  the  rate  being 
given  in  watts  per  cubic  inch,  or  in  kilowatts  per  cubic  foot.} 

In  Moissan's  small  furnace,  (Fig.  6,  p.  8),  which  was  com- 
posed ol  blocks  of  quicklime,  he  employed  35  to  40  amperes  at 
55  volts,  direct  current;  or  1,925  to  2,200  watts. §  The  interior 
cavity  of  the  furnace  was  about  1.75  inches  in  diameter,  and  about 
1.7  inches  in  height,  corresponding  to  a  volume  of  4.1  cubic  inches. 
The  watts  per  cubic  inch  will,  therefore,  be  470  to  538,  or  say  500 

*Borrhcrs'    Klrctric    Smelting    and   Refining,    (1897    Ed.).      Figs.    157,    158,    and    165. 
fBorchers'    Electric   Smelting   and   Refining,   (1897  YA.).     Fig.    86. 
Ji    Watt    per    cubic    inch  =  1.728    Kilowatts    per    cubic    foot. 
£11.    Moissan,   The    Electric   Furnace,    p.    5. 


CONSTRUCTION    AND    DESIGN.  t)I 

as  a  round  figure.  Some  allowance  should  be  made  for  the  heat 
produced  in  the  electrodes  themselves,  and  this  would  leave  per- 
haps 400  or  450  watts  per  cubic  inch  for  the  interior  of  the  furnace 
This  figure,  as  will  be  seen  directly,  is  about  one  hundred  times 
as  great  as  the  usual  rate  of  heating  in  a  fair-sized  electric  furnace, 
as  used  for  steel  making,  for  instance. 

Moissan's  electric  tube  furnace,  contained  a  carbon  tube  in 
which  the  material  to  be  heated  was  placed,  and  the  furnace  itself 
was  composed  of  limestone,  and  was  lined  with  alternate  layers  of 
carbon  and  magnesia.  In  this  furnace  he  employed  300  amperes 
at  70  volts  (  =  21,000  watts),  or  1,000  amperes  at  60  volts,  (  =  60,- 
ooo  watts). *  The  dimensions  of  the  interior  of  the  furnace,  assum- 
ing that  his  perspective  drawings  are  to  scale,  would  be  4.4  inches 
long,  3.2  inches  wide,  and  4  inches  high;  corresponding  to  a 
volume  of  56  cubic  inches.  The  watts  per  cubic  inch  wrould 
vary  from  380  to  1,100.  A  deduction  for  the  heat  produced  in  the 
electrodes  themselves  would  reduce  these  figures  by  10%  or  20%. 

An  even  more  intense  rate  of  heating  is  mentioned,  in  which 
he  employs  1,200  to  2,000  amperes  at  100  volts  in  an  unlined 
limestone  furnace. t  The  internal  diameter  is  stated  to  be  4  inches, 
and  assuming  the  height  to  be  the  same,  the  volume  of  the  cavity 
would  be  50  cubic  inches.  The  watts  supplied  would  be  120,000 
to  200,000,  or  2,400  to  4,000  watts  per  cubic  inch.  The  operation 
of  this  furnace  is  only  of  short  duration,  the  lime,  produced  by 
heating  the  interior  of  the  limestone  blocks,  soon  melting,  and 
running  like  water,  while  vaporized  lime  roars  out  around  the 
electrodes,  and  the  furnace  is  soon  destroyed.  The  temperature 
produced  was  limited  by  the  rapid  melting  and  vaporizing  of  the 
lime,  but  by  supplying  the  heat  at  such  an  enormous  rate,  the 
greater  part  of  the  cavity  might  well  be  considerably  hotter  than 
the  boiling  temperature  of  melted  lime. 

The  small  furnace,  first  mentioned,  could  be  used  for  longer 
periods,  as  the  rate  of  heat  production  was  so  much  less,  and  the 
furnace  was  therefore  less  rapidly  destroyed ;  while  the  tube 
furnace,  lined  with  carbon  and  magnesia,  could  be  run  continu- 
ously. 

The  Stassano  steel  furnace,  (Fig.  37,  p.  130),  resembles  the 
Moissan  furnace,  as  the  ore  to  be  smelted  is  heated  by  radiation 
from  an  arc.  The  furnace  described  by  Dr.  Goldschmidt  in 
1903,1  which  is  somewhat  larger  than  the  one  figured  in  Dr. 

*H.  Moissan,  The  Electric  Furnace,  p.  17. 
•f-H.  Moissan,  The  Electric  Furnace,  p.  14. 
^Electrochemical  Industry,  vol.  i.,  p.  247. 


62  THE     ELECTRIC     FURNACE. 

Haanel's  Report,*  took  an  alternating  current  of  2,000  amperes 
at  170  volts,  and  used  about  450  horse-power.  The  horse-power 
corresponds  to  336  kilo-watts,  but  part  of  this  would  be  wasted 
outside  the  furnace.  The  volt-amperes  are  340,000,  and  assuming 
a  power-factor  of  0.75  this  would  give  255  kilowatts  consumed  in 
the  furnace.  The  interior  of  the  furnace  was  about  40  inches 
cube,  or  64,000  cubic  inches,  giving  4  watts  per  cubic  inch,  or 
6.9  kilowatts  per  cubic  foot.  The  difference  between  this  rate  of 
heating  and  that  employed  by  Moissan,  depends  in  part  upon  the 
lower  temperature  required,  in  part,  upon  the  great  loss  of  heat  in 
the  Moissan  furnace,  produced  by  the  vaporizing  of  the  materials  of 
the  furnace,  and  in  part  upon  the  larger  size  and  better  heat  re- 
taining construction  of  the  Stassano  furnace. 

The  Heroult  steel  furnace  at  La  Praz,  (Fig.  23,  p.  87), 
figured  by  Dr.  Haanel,t  is  about  7  feet  long,  4  feet  wide,  and  2 
feet  high  inside,  giving  a  volume  of  56  cubic  feet.  The  power 
employed  was  353  kilowatts,  J  or  6.3  kilowatts  per  cubic  foot, 
which  agrees  well  with  the  Stassano  furnace. 

The  furnace  recently  employed  at  Sault  Ste.  Marie,  for 
smelting  Canadian  iron  ores,  (Fig.  29,  p.  108),  had  an  interior 
volume  of  18.4  cubic  feet,  and  consumed  about  166  kilowatts  of 
electrical  power,  or  9  kilowatts  per  cubic  foot.§  This  is  only  a 
little  larger  than  the  figures  for  the  Heroult  steel  furnace: — 6.3 
kilowatts  per  cubic  foot,  and  the  Stassano  furnace, — 6.9  kilowatts 
per  cubic  foot ;  but  the  meaning  of  the  figure  is  not  quite  the  same. 
The  whole  interior  of  the  Stassano  and  Heroult  steel  furnaces  is 
heated  to  about  the  melting  temperature  of  the  steel,  and  the 
rate  of  heat  production  for  each  cubic  foot  of  the  furnace  is  of 
the  first  importance  in  determining  the  temperature  to  which  the 
furnace  can  be  heated.  In  the  Heroult  ore-smelting  furnace, 
however,  the  temperature  is  far  from  uniform  throughout  the  in- 
terior, only  the  lower  part  being  heated  to  a  smelting  temperature  ; 
and  the  volume  of  the  upper  part  of  the  furnace,  where  the  ore  is 
gradually  heated  during  its  descent  to  the  smelting  zone,  could 
be  very  much  greater  without  the  change  having  any  material 
effect  upon  the  temperature  in  the  smelting  zone  of  the  furnace. 
In  such  a  furnace  it  is  consequently  of  little  importance  to  con- 
sider the  total  volume  in  relation  to  the  electrical  power,  a  more 
significant  figure  being  obtained  by  dividing  the  kilowatts  by  the 

'European  Commission  Report,  p.  n  and  Figs.  9  and  10 
fEuropean  Commission  Report,  p.  5  and  Figs.  3  and  4. 
tEuropean  Commission  Report,  p.  53. 

§Dr.    Haanel,    Report   on    Experiments    at    Sault    Ste.    Marie,    1907,    p.    46,    and    plate 
vii.      (Also    in    the    "Canadian    Engineer,"   vol.    xiii.,    pp.    221    and    254). 


CONSTRUCTION    AND    DESIGN.  63 

volume  in  cubic  feet  of  the  fusion  or  smelting  zone  of  the  furnace. 
This  zone  is  necessarily  difficult  to  define,  but  assuming  that  the 
electrode,  C,  in  Fig.  29,  is  in  its  normal  working  position,  the 
smelting  zone  would  occupy  about  7  cubic  feet,  making  the 
electrical  power  24  kilowatts  per  cubic  foot  of  the  zone. 

The  rate  of  heating,  in  the  smelting  zone  of  this  furnace,  is 
very  much  greater  than  in  a  steel  furnace,  and  this  is  explained 
by  the  constant  supply  of  cooler  material  which  absorbs  most  of 
the  heat.  The  efficiency  will  tend  to  increase  as  the  furnace  is 
driven  faster ;  but,  with  the  more  rapid  smelting,  the  zone  of 
fusion  will  become  enlarged,  thus  corroding  the  walls  of  the 
furnace.  There  is  consequently  a  limit  beyond  which  it  is  not  de- 
sirable to  increase  the  rate  of  heating  in  electric  furnaces. 

The  Keller  furnace,  (Fig.  30,  p.  112),  consists  of  two  smelt- 
ing shafts,  with  a  common  reservoir  for  the  molten  products. 
Taking  the  dimensions  from  Figs,  n  and  12  of  Dr.  Haanel's 
European  report,  the  smelting  zone,  AB,  of  each  shaft,  omitting 
the  connecting  passage,  CO,  which  acts  as  a  reservoir  for  the 
fused  iron  and  slag,  will  occupy  about  19  cubic  feet.  The  power 
used,  in  the  first  run  of  furnaces,  Xos.  n  and  12,  was  613  kilo- 
watts,* or  306  kilowatts  for  each  of  the  two  shafts.  This  is 
equal  to  16  kilowatts  for  each  cubic  foot  of  the  fusion  zone.  If 
the  whole  volume  of  the  shaft  were  considered,  the  power  would 
correspond  to  5  kilowatts  per  cubic  foot,  or  to  6  kilowatts  per  cubic 
foot  of  the  shaft  up  to  the  level,  FG,  at  which  the  gases  escape 
from  the  furnace. 

These  figures  are  less  than  were  obtained  from  the  Heroult 
furnace,  the  difference  being  due  mainly  to  the  larger  size  of  the 
Keller  furnace,  in  which  the  smelting  zone  was  three  times  as 
large  as  in  the  Heroult  furnace.  The  larger  size  of  the  Keller 
furnace  occasioned  a  smaller  loss  by  radiation  and  conduction  per 
cubic  foot,  and  a  correspondingly  smaller  rate  of  heat  production 
was  required.  In  this  connection  it  should  be  mentioned,  that 
the  rate  of  smelting,  per  cubic  foot  of  smelting  zone,  in  the 
Keller  furnace,  was  less  than  one-third  of  the  rate  of  smelting  in 
the  Heroult  furnace,  while  the  consumption  of  electrical  energy 
per  ton  of  pig-iron  was  twice  as  great  in  the  Keller  furnace  as  in 
the  Heroult  furnace.  This  seems  to  indicate  that  the  supply  of 
power  in  the  Keller  furnace  was  not  quite  sufficient,  but 
as  this  furnace  was  working  badly  as  a  result  of  a 
shut-down,  it  is  unsafe  to  draw  deductions  from  its  rate 
of  smelting. 


*Dr.    Haanel's    European    Report,    1904,    p.    40. 


64  THE     ELECTRIC     FURNACE. 

Better  results  were  obtained  in  the  second  run,  with  the 
Keller  furnaces  Nos.  i  and  2.*  These  were  stated  to  be  identical 
with  Nos.  ii  and  12,  with  the  exception  of  the  connecting  channel, 
which  was  absent  in  Xos.  i  and  2.  Assuming  the  smelting  zone 
to  be  of  the  same  size,  the  rate  of  heat  production  would  be  only 
6  kilowatts  per  cubic  foot  of  this  part  of  the  furnace.  The  energy 
consumption  per  ton  of  pig-iron,  in  these  furnaces,  was  a  little  less 
than  in  the  Heroult  furnace. 

In  the  Kjellin  steel  furnace,  (Fig.  24,  p.  93),  no  electrodes 
are  employed;  the  steel  is  contained  in  a  ring-shaped  trough,  and 
is  melted  by  an  electric  current  which  is  induced  in  the  steel  just 
as  it  is  in  the  secondary  windings  of  a  transformer. 

The  furnace  shown  in  Dr.  Haanel's  report, t  has  a  trough  of 
13  cubic  feet  capacity.  The  power  delivered  to  the  primary  of 
the  transformer  was  150  kilowatts.  Assuming  the  transformer 
losses  to  be  10%  of  this,  135  kilowatts  would  be  supplied  to  the 
molten  steel,  or  10  kilowyatts  per  cubic  foot  of  the  furnace. 

This  figure  is  larger  than  in  the  Heroult  steel  furnace,  and 
the  difference  may  be  partly  accounted  for  by  the  larger  amount  of 
waste  space  in  the  latter  furnace.  The  efficiency  of  the  Kjellin 
furnace  is  low,  on  account  of  the  small  cross  section  (6"  by  18") 
of  the  trough  containing  the  molten  steel ;  and  a  somewhat  small 
cross  section  appears  to  be  necessary  in  this  type  of  furnace. 

The  Gin  steel  furnace,  (Fig.  28,  p.  104),  resembles  the  Kjellin 
furnace  in  consisting  of  a  long  trough  or  canal,  of  small  cross 
section,  containing  the  molten  steel ;  but  the  electric  current  is  in- 
troduced at  the  ends  of  the  trough  through  water-cooled  steel 
terminals.  In  order  to  reduce  the  loss  of  heat,  the  canal  is  folded 
upon  itself  like  the  filament  of  an  incandescent  lamp. 

Mr.  Gin  calculates  the  dimensions  for  a  number  of  furnaces, 
in  a  paper  that  has  been  printed  in  Dr.  Haanel's  report. t  For  a 
700  kilowatt  furnace,  the  volume  of  the  steel  in  the  trough  would 
be  19.5  cubic  feet,  and  assuming  the  trough  to  be  half  filled  by 
the  molten  steel,  its  capacity  would  be  39  cubic  feet,  correspond- 
ing to  1 8  kilowatts  per  cubic  foot  of  the  trough.  The  trough 
would  be  nearly  30  feet  long,  9^"  wide,  ig1/^"  deep,  and  half  full 
of  molten  steel. 

In  the  Acheson  furnaces,  Figs.  8,  and  38-41,  the  heat  is 
produced  by  the  passage  of  an  electric  current  through  a  central 


*Dr.    Haanel's    European   Report,   1904,    p.    44. 

•f-Dr.    Haanel's    European    Report,    1904,   p.    2    and    Fig. 

tDr.    Haanel's   European  Report,    1904,    p.    173. 


CONSTRUCTION    AND    DESIGN.  65 

core  or  through  the  charge  itself.  The  charge  does  not  melt, 
and  remains  nearly  in  the  same  position  until  the  end  of  the  opera- 
tion. Very  little  data  is  available  with  regard  to  the  actual  work- 
ing of  these  furnaces.  The  following  examples  may  be  given  : — 

In  a  patent  by  E.  G.  Acheson*  for  a  method  of  making  carbon 
articles  of  a  high  density  and  conductivity  by  heating  them  in  an 
electric  furnace  without  reaching  the  point  of  graphitization,  the 
furnace  is  stated  to  be  30  feet  long,  30  inches  wide,  and  10  inches 
deep  inside.  The  power  used  was  about  750  kilo-volt-amperes. 
Assuming  the  power  factor  to  be  0.9  this  would  correspond  to  10 
or  1 1  kilowatts  per  cubic  foot  of  the  furnace. 

The  Acheson  graphite  and  electrode  furnaces  are  described 
by  F.  A.  J.  FitzGeraldt  who  takes  the  data  in  part  from  Acheson 's 
patents.  The  graphite  furnace  is  said  to  be  30  feet  long,  14 
inches  wide,  and  18  inches  deep,  thus  having  a  volume  of  52^2 
cubic  feet.t-  The  current  at  the  beginning  of  the  run  is  stated 
to  be  300  amperes  at  200  volts,  and  FitzGerald  assumes  that 
when  the  furnace  has  become  heated  it  absorbs  750  kilowatts. 
The  latter  figure  would  correspond  to  14  kilowatts  per  cubic  foot. 
In  the  electrode  furnace,  the  length  between  terminals  is  30  feet, 
and  the  cross  section  of  the  piles  of  electrodes  under  treatment  is 
24  inches  by  17  inches.  Allowing  a  few  inches  of  granular 
carbon  around  the  electrodes,  the  volume  of  the  furnace  would  be 
150  cubic  feet,  700  kilowatts  were  employed,  corresponding  to  less 
than  5  kilowatts  per  cubic  foot.  If  no  allowance  were  made  for 
the  granular  carbon,  the  rate  of  heating  would  be  8  kilowatts  per 
cubic  foot  of  the  charge. 

A  drawing  of  the  carborundum  furnace§  shows  it  to  be  16^2 
feet  long,  6  feet  wide,  and  5^  feet  high  inside.  The  power  used 
is  750  kilowatts,  which  is  only  i  y^  kilowatts  per  cubic  foot.  If, 
however,  it  is  considered  that  part  of  the  charge  in  the  furnace 
serves  as  a  heat  retaining  wall,  and  the  calculation  is  limited  to  that 
portion  of  the  charge  which  is  converted  into  carborundum,  the 
rate  of  heating  is  found  to  be  3  kilowatts  per  cubic  foot. 


*E.   G.  Acheson,  U.S.   patent  749,418,  see  Electrochemical  Industry,  vol.  ii.,  p.  108. 

•j-The  Ruthenburg  and  Acheson  Furnaces,  F.  A.  J.  FitzGerald,  Electrochemical 
Industry,  vol.  iii.,  p.  416. 

JE.  G.  Acheson,  U.S.  patent  711,031,  see  Electrochemical  Industry,  vol.  i.,  p.  130. 
The  author  has  been  informed  by  the  Acheson  Graphite  Company  that  these  dimen- 
sions are  incorrect.  If  as  seems  reasonable  to  suppose  the  cross  section  for  a  750 
kilowatt  furnace  is  somewhat  larger  than  stated  above,  the  rate  of  heating  would 
be  proportionately  reduced,  and  would  agree  more  nearly  with  the  other  figures  for 
this  class  of  furnace. 

§The  Carborundum  Furnace,  F.  A.  J.  FitzGerald,  Electrochemical  Industry,  vol. 
iv-,  p.  53- 


66  THE     ELECTRIC     FURNACE. 

Collecting  the  results  obtained  above  for  the  power  required 
per  cubic  foot  of  electric  furnace,  the  following  general  figures 
may  be  given  for  moderate  or  large  sized  furnaces,  using  from 
200  to  1,000  horse-power: — Steel  melting  furnaces,  such  as  the 
Heroult  and  Stassano  furnaces,  employ  5  to  8  kilowatts ;  steel 
melting  furnaces  such  as  the  Gin  or  Kjellin  furnaces  employ  10  to 
20  kilowatts  ;  ore  smelting  furnaces,  such  as  those  of  Keller  and 
Heroult,  employ  about  10  to  20  kilowatts  per  cubic  foot  of  the 
zone  of  fusion  ;  and  the  power  used  in  furnaces  of  the  Acheson 
type  varies  from  about  3  kilowatts  in  the  carborundum  furnace  to 
about  10  kilowatts  in  the  graphite  furnace.  Small  sized  furnaces 
for  electric  smelting  may  employ  as  much  as  30  to  100  kilowatts 
per  cubic  foot,  and  Moissan  used  no  less  than  500  to  5,000  kilo- 
watts of  electrical  power  per  cubic  foot  of  his  furnaces. 

Voltage  Required  for  Electric  Furnaces. 

Having  determined  how  many  watts  should  be  supplied  to  the 
furnace,  the  voltage  of  the  supply  must  next  be  considered.  The 
watts  supplied  are,  for  direct  current,  the  product  of  the  amperes 
and  the  volts,  while  for  alternating  current  they  are  somewhat  less ; 
the  product  of  volts  and  amperes  being  multiplied  by  a  factor — 
the  power  factor — which  varies  from  about  0.7  to  0.9  in  different 
forms  of  furnace,  in  order  to  obtain  the  watts.  The  heat  pro- 
duced depends  simply  upon  the  product  of  volts,  amperes  and 
power  factor,*  so  that  it  would  appear  possible  to  use  either  a 
high  or  low  voltage,  provided  the  watts  were  sufficient.  If  a 
moderate  current  at  a  high  voltage  could  be  employed,  it  would 
be  a  great  convenience,  but  this  is  usually  impracticable,  because 
it  is  not  generally  feasible  to  construct  a  furnace  having  a  suf- 
ficiently high  electrical  resistance. 

The  whole  problem  turns  upon  the  electrical  resistance  of  the 
resistor  R,  (Fig.  21).  Suppose  that  a  furnace  needs  250  kilo- 
watts to  heat  it,  then,  taking  direct  current  for  simplicity,  in 
illustration,  if  the  furnace  resistance  were  i  ohm,  a  500  volt  supply- 
would  drive  a  current  of  500  amperes  through  the  furnace  and 
would  develop  the  necessary  250  kilowatts.  If,  however,  the 
furnace  had  a  resistance  of  only  o.oi  ohm,  the  current,  in  amperes, 
would  be  one  hundred  times  the  volts,  and  5,000  amperes  at  50 
volts  would  be  needed.  The  latter  case  is  approximately  that  of 

*Assuming    that    all    the    energy    is    converted    into    heat,    and    none    of    it    spent    in 
chemical    work,    such    as    electrolysis. 


CONSTRUCTION    AND    DESIGN.  67 

the  experimental  Heroult  furnace  used  by  Dr.  Haanel,  and  shows 
what  enormous  currents  will  have  to  be  supplied  to  electric-smelt- 
ing furnaces,  if  constructed  on  any  considerable  scale,  since  the 
amperes  increase  with  the  size  of  the  furnace  far  more  rapidly 
than  the  volts.  The  use  of  such  enormous  currents  is  incon- 
venient and  increases  considerably  the  cost  of  cables,  transform- 
ers, electrodes  and  electrode-holders. 

Voltage  of  Arc  Furnaces. — The  voltage  of  a  resistance  furnace 
is  nearly  proportional  to  the  current  flowing  through  it.  To 
double  the  current,  nearly  twice  the  voltage  would  be  needed, 
but  in  the  arc  furnace  (except  perhaps  in  the  Moissan  furnace, 
which  is  so  small  that  the  arc  fills  the  furnace)  the  voltage  does 
not  increase  considerably  with  increase  of  current,  and  the  voltage 
of  the  arc  itself  is  often  less  as  the  current  increases.  This 
sounds  impossible  but  it  is  a  well  established  fact,  and  points  to 
the  instability  of  the  arc  unless  a  steadying  resistor  is  placed  in 
series  with  it.  In  a  large  furnace  the  resistance  of  the  cables, 
electrodes  and  transformer  or  dynamo  is  usually  sufficient  for  the 
purpose,  but  the  writer  has  frequently  extinguished  the  arc  in 
an  experimental  furnace  by  turning  on  too  much  current,  that  is 
by  cutting  out  too  much  of  the  regulating  rheostat,  and  so  apply- 
ing too  high  a  voltage  to  the  arc.  The  resistance  of  an  arc  is 
net  constant,  but  as  the  current  increases  the  arc  becomes  larger 
in  cross  section  and  its  resistance  decreases  in  about  the  same  pro- 
portion, or  even  faster  than  the  current  increases;  the  voltage  in 
consequence  remains  constant  or  decreases. 

A  certain  minimum  voltage,  which  varies  from  about  25  to  35, 
is  needed  in  order  to  start  an  arc  at  all ;  beyond  this  the  voltage 
increases  with  the  length  of  the  arc,  on  account  of  the  additional 
resistance  that  is  introduced  as  the  carbons  are  drawn  farther 
apart.  The  voltage  of  an  ordinary  lighting  arc  may  be  obtained 
by  the  formula  : — 

E  =  m  +  nl. 

E  is  the  voltage,  1  is  the  length  of  the  arc  in  inches,  and  m  and  n 
are  constants,  which  for  good  pure  carbons  have  the  values  40.6 
and  40  respectively.*  The  constants  would  be  smaller  for  arcs 
between  cored  carbons,  for  arcs  enclosed  in  a  furnace,  so  that 
the  heat  of  the  arc  was  retained,  and  for  alternating  current  arcs. 
The  following  figures,  may  be  given  as  examples  of  direct  current 
arcs  in  small  furnaces ;  they  have  been  selected  from  the  work  of 
Henri  Moissan,  whose  furnace  is  shown  in  Fig.  6,  page  8. 


*Electric  Lighting,  by  F.   B.   Crocker,  vol.   ii.,  p.   308. 


68  THE     ELECTRIC     FURNACE. 

TABLE  VII. 
Voltage  of  Moissan's  Arc  Furnace. 

Amperes.        Volts.  Amperes.  Volts. 

35-4° 55  8o° II0 

ioo 45  900 45 

250 70,  75  1,000. 50,  60,  70,  80,  no 

300 60,  70,    85      1,200 70,  100,   no 

400 80  2,000 60,  80,  100 

45° 6o>  75  2,200 60,  70 

600 60 

This  table  indicates  that  the  voltage  of  the  arc  is  not  de- 
termined by  the  amount  of  current  flowing  through  the  furnace, 
but  depends  mainly  upon  the  length  of  arc  and  the  kind  of  vapour 
present  in  the  furnace.  The  length  of  arc  is  unfortunately  not 
given,  but  probably  varied  from  about  half  an  inch  to  two  inches 
or  three  inches ;  aluminium  vapour  is  mentioned  as  giving  a  long 
arc  of  two  inches  to  two  and  a  half  inches,  and  the  2,000  and  2,200 
ampere  arcs  at  60  volts  were  obtained  in  the  presence  of  iron 
vapour.  The  actual  volts  across  the  arc  will  be  somewhat  less 
than  the  figures  given,  on  account  of  the  drop  of  volts  along  the 
electrodes  as  well  as  in  the  connections.  This  drop  is  quite  con- 
siderable in  the  case  of  heavy  currents,  and  would  vary  from 
about  5  to  20  or  even  30  volts  depending  on  the  current  and  the 
size  of  carbon  employed. 

The  alternating  current  is  generally  used  in  arc  furnaces  in- 
tended for  industrial  use  and  the  Heroult  and  Stassano  steel 
furnaces  may  be  taken  as  examples. 

The  Stassano  furnace,  (Fig  37),  resembles  the  Moissan 
furnace  in  general  construction.  A  long  arc,  GH,  is  maintained 
between  the  ends  of  somewhat  slender  electrodes,  and  when  the 
furnace  becomes  thoroughly  hot,  the  arc  may  be  drawn  out  until 
it  traverses  the  whole  width  of  the  furnace.  In  one  furnace*  the 
width  was  39",  and  an  alternating  current  arc  of  2,000  amperes 
at  170  volts  was  used.  It  will  be  seen  that  this  voltage  is  very 
much  lower  than  would  be  required  by  the  formula  given  above ; 
the  high  temperature  of  the  furnace,  the  presence  of  metallic  and 

"Electrochemical    Industry,    vol.    i.,    (1903),    p    247. 


CONSTRUCTION    AND    DESIGN.  69 

other  vapours,  and  the  use  of  alternating  instead  of  direct  current 
all  contribute  to  this  effect. 

The  Heroult  furnace,  as  shown  in  Fig.  23,  resembles  a  Well- 
man  tilting  open-hearth  furnace  from  which  the  gas  and  air  ports 
have  been  removed,  and  two  large  carbon  electrodes,  C,  C,  enter 
through  holes  in  the  roof.  The  furnace  is  basic  lined,  but  it 
would  be  possible  to  employ  an  acid  lining.  The  arc  does  not 
play  from  one  carbon  to  the  other,  as  in  the  Moissan  and  Stassano 
furnaces,  but  there  is  an  arc  between  each  electrode  and  the  slag 
and  metal  immediately  beneath  it.  In  this  way  the  heat  of  the 
arc  is  directly  communicated  to  the  metal,  and  as  two  arcs  are 
produced  in  series,  the  voltage  of  the  furnace  will  be  twice  as 
great  as  that  of  a  single  arc.  The  furnace  seen  by  the  Com- 
mission at  Kortfors  took  4,000  amperes  at  125  volts,  the  power 
supplied  being  about  450  kilowatts,*  while  the  smaller  furnace  at 
La  Praz  took  about  4,000  amperes  at  108  volts.  The  power 
supplied  was  350  kilowatts,  but  the  current  was  not  measured. t 
The  voltage  of  each  arc  in  these  furnaces  will  be  about  45  or  55, 
and  the  arc  will  be  quite  short,  the  carbons  being  kept  just  clear 
of  the  slag. 

Voltage  of  Resistance  Furnaces. — Resistance  furnaces  have 
usually  a  lower  voltage  than  arc  furnaces  of  the  same  size.  The 
Heroult  Ore-Smelting  Furnace  (Fig.  29)  is  of  the  resistance  type, 
as  no  arc  is  formed ;  the  current  flowing  between  the  movable 
electrode  C,  and  the  carbon  lining  at  the  bottom  of  the  furnace, 
through  the  solid  and  liquid  materials  in  the  smelting  zone.  The 
electrical  resistance  of  these  materials  causes  the  energy  of  the 
current  to  be  converted  into  heat  and  largely  determines  the  volt- 
age of  the  furnace;  the  voltage  being  higher  for  a  given  current, 
if  the  contents  of  the  furnace  have  a  higher  electrical  resistance. 
In  the  recent  experiments  with  this  furnace,  only  36  volts  were  re- 
quired to  maintain  an  alternating  current  of  5,000  amperes. t 

The  Keller  Ore-Smelting  Furnace  (Fig.  30)  is  equivalent  to 
two  Heroult  furnaces,  with  a  connecting  passage  between  the 
crucibles  of  the  twro  furnaces.  This  passage  serves  as  a  reservoir 
for  the  molten  slag  and  iron,  and  also  serves  to  connect  electrically 
the  molten  metal  at  the  bottom  of  each  furnace ;  an  alternative 
passage  for  the  current,  in  case  the  reservoir  were  emptied  at  any- 
time, is  provided  through  the  carbon  plugs  BE,  B'E1,  and  copper 
connector  EE1.  Electrically,  the  two  furnaces  are  arranged  in 


*Dr.   Haanel,   European  Report,    1904,   p.    52. 

•f-Dr.    Haanel,   European   Report,   1904,    p.    54. 

fDr.    Haanel,  Report  on   Experiments   at   Sault   Ste.    Marie,    1907,   p.    52. 

6 


J-0  THE     ELECTRIC     FURNACE. 

series,  the  current  being  supplied  through  the  two  movable 
electrodes  DA,  D'A1,  and  passing  in  series  through  the  two 
smelting  zones,  AB,  A1!*1 ;  and  the  voltage  is  in  consequence  twice 
as  great  as  it  would  be  in  a  single  furnace  of  the  Heroult  type. 
In  the  experiments  made  by  Dr.  Haanel  at  Livet,*  the  double 
shaft  furnace,  Nos.  n  and  12,  took  a  current  of  11,000  amperes 
at  59  volts,  and  the  double  furnace,  Nos.  i  and  2,  took  7,250 
amperes  at  55.3  volts. 

For  a  given  size  and  shape  of  furnace,  and  distance  between 
the  electrodes  and  the  molten  iron  in  the  bottom  of  the  furnace, 
the  voltage  of  the  furnace  will  increase  with  the  current  that  is 
passed  through  it.  The  voltage  will  increase  less  rapidly  than 
the  current,  however,  because  at  the  higher  temperatures  pro- 
duced by  the  increased  current,  the  electrical  resistance  of  the 
furnace  contents  will  be  less  than  it  was  with  the  smaller  current, 
and  so  the  ratio  of  voltage  to  current  will  be  reduced.  If  the 
cross  section  of  the  furnace  were  increased,  so  that  the  current 
density  remained  constant,  i.e.,  the  number  of  amperes  for  each 
square  foot  of  cross  section  of  the  furnace  was  the  same  as  before, 
the  voltage  would  remain  constant ;  and  if  the  height  of  the  furnace 
and  the  distance  between  the  movable  electrode  and  the  bottom 
of  the  shaft  were  increased  proportionately,  the  voltage  would 
increase  in  the  same  ratio.  That  is  to  say,  in  furnaces  of  similar 
shapes,  but  of  different  dimensions  and  for  constant  current 
densities,  the  voltage  will  be  proportional  to  the  linear  dimensions, 
and  the  current  will  be  proportional  to  the  square  of  these 
dimensions.  It  follows  from  this,  that  the  voltage  is  proportional 
to  the  square  root  of  the  current,  and  as  the  size  of  electric 
furnaces  is  increased,  the  voltage  necessary  to  operate  them  will 
also  increase  ;  but  with  far  less  rapidity  than  the  electrical  current 
which  must  be  supplied.  In  practice,  the  voltage  will  tend  to 
increase  less  rapidly  than  the  dimensions  of  the  furnace ;  because 
in  large  furnaces  the  same  current  density  would  produce  a  rather 
higher  temperature,  and  so  would  make  the  charge  a  better 
electrical  conductor,  or  smaller  current  densities  could  be  em- 
ployed which  would  need  a  lower  voltage. 

The  voltage  of  an  ore-smelting'  furnace  of  the  Keller  or 
Heroult  type,  depends  mostly  upon  the  height  to  which  the 
electrode  is  raised  from  the  bottom  of  the  furnace,  and  this  can 
be  easily  changed  during  the  smelting  operation,  thus  affording  a 
convenient  means  of  regulating  the  electric  current.  If  the  current 
were  supplied  to  such  a  furnace  at  an  absolutely  constant  voltage, 

*Dr.   Haanel,   European  Report,   1904,   p.    36. 


CONSTRUCTION    AND    DESIGN.  71 

any  change  in  the  resistance  of  the  furnace  would  lead  to  a  change 
in  the  amount  of  current,  the  voltage  remaining  constant ;  and  in 
running  a  furnace  under  such  conditions,  the  electrode  would  be 
lowered  to  increase  the  current,  and  raised  to  decrease  it.  In 
practice,  the  voltage  at  the  furnace  terminals  is  not  absolutely 
constant,  but  decreases  with  an  increase  of  current,  on  account 
of  the  resistance  of  cables,  transformers,  etc.  ;  and,  in  conse- 
quence, the  volts  and  amperes  supplied  to  a  furnace  will  usually 
vary  in  opposite  directions.  This  refers,  of  course,  to  changes 
in  the  current  produced  by  changes  in  the  furnace  itself ;  external 
changes  such  as  a  change  in  the  speed  of  the  dynamo  supplying 
the  current  would  reduce  or  increase  both  the  volts  and  the 
amperes.  The  drop  of  voltage  that  accompanies  an  increase  of 
current  is  not  objectionable  in  electric  smelting,  and  it  serves  to 
some  extent  as  an  automatic  regulator  of  the  current. 

Regulation  of  Electric  Smelting. 

This  is  usually  effected  by  electric  motors  which  raise  or  lower 
the  movable  electrodes.  The  motors  are  started,  stopped,  and 
reversed,  by  instruments  operated  by  the  voltage  of  the  furnace, 
in  such  a  manner  as  to  keep  this  constant.  In  the  Keller  furnace, 
Fig.  30,  and  the  Heroult  steel  furnace,  Fig.  23,  there  are  two 
movable  electrodes ;  each  of  these  being  independently  regulated 
so  as  to  keep  a  constant  voltage  between  itself  and  the  molten 
metal  in  the  furnace.  The  automatic  regulating  apparatus  for 
the  Heroult  furnace  is  described  in  Dr.  Haanel's  report.* 

The  change  in  electrical  resistance  due  to  a  change  in  the 
height  at  which  the  electrode  is  kept  in  a  smelting  furnace,  affords 
a  means  of  adapting  the  furnace  to  a  variety  of  voltages. 
Electrically,  it  is  advantageous  to  operate  the  furnace  at  as  high 
a  voltage  as  it  will  take,  and  it  is,  therefore,  important  to  ascer- 
tain how  high  the  electrode  can  be  raised  without  causing  trouble 
in  the  furnace.  The  exact  height  that  is  most  desirable  will  de- 
pend upon  a  number  of  factors,  such  as  the  shape  of  furnace, 
size  of  electrode,  nature  of  the  charge,  and  amount  of  current, 
but  the  distance  between  the  electrode  and  the  molten  slag  in 
shaft  smelting  furnaces  should  probably  be  less  than  the  width 
of  the  crucible  of  the  furnace. 

In  other  types  of  resistance  smelting  furnaces,  the  current 
passes  through  the  molten  slag  and  metal,  instead  of  through  the 
melting  ore,  the  current  entering  by  means  of  two  or  more  carbon 


*Dr.   Haanel,   European  Report,    1904,   p.  6. 


72  THE     ELECTRIC     FURNACE. 

electrodes  which  dip  into  the  fused  slag,  as  in  the  Harmet  furnace, 
(Fig.  31);  by  electrodes  of  fused  metal  lying  beneath  the  slag,  as 
in  the  Laval  furnace,  (Fig.  18);  or  by  induction,  without  the  use 
of  electrodes,  as  in  the  Snyder  furnace,  (Fig.  47).  In  such  furnaces, 
the  slag  becomes  heated  above  its  melting  temperature,  by  the 
passage  of  the  current,  and  melts  or  dissolves  the  ore  which  rests 
upon  it.  The  voltage  depends  upon  the  shape  and  size  of  the 
furnace,  but  on  account  of  the  low  specific  resistance  of  molten 
slags  it  will  usually  be  lower  than  in  furnaces  in  which  the  current 
passes  through  the  melting  ore,  as  well  as  through  the  fused  slag. 
The  molten  metal  accumulating  in  the  bottom  of  the  furnace  will 
also  tend  to  lower  the  voltage,  by  carrying,  on  account  of  its 
greater  conductivity,  a  large  part  of  the  current.  Furnaces,  in 
which  the  electrodes  dip  into  the  fused  slag,  are  also  less  easily 
regulated,  and  changes  in  the  amount  of  molten  slag  and  metal 
affect  very  greatly  the  amount  of  current  that  flows  through  such 
furnaces. 

In  the  Kjellin  and  Gin  furnaces,  the  electrical  resistance  of 
the  steel  itself  is  relied  upon  for  converting  the  energy  of  the 
current  into  heat.  The  specific  resistance,  or  resistivity,  of  steel, 
even  when  molten,  is  so  small  that  the  metal  must  be  contained 
in  a  trough  or  canal  of  considerable  length  and  moderate  cross 
section,  in  order  to  obtain  any  appreciable  electrical  resistance, 
and  even  then,  the  voltage  is  very  small,  and  enormous  currents 
must  be  supplied,  in  order  to  heat  the  furnaces.  In  the  Kjellin 
furnace,  already  referred  to,  a  current  of  30,000  amperes  is  sup- 
posed to  circulate  around  the  ring  of  mol-ten  steel,  the  voltage  re- 
quired to  drive  such  a  current  being  only  7.  In  the  Gin  furnace, 
the  voltage  is  also  very  small,  the  calculations  already  referred  to 
being  for  an  electrical  supply  at  15  volts,  the  currents  ranging 
from  10,000  to  100,000  amperes.  Furnaces  of  such  low  resist- 
ance are  very  unsatisfactory  electrically ;  but  the  absence  of  car- 
bon electrodes,  and  the  production  of  the  heat  directly  in  the 
molten  steel,  render  them  very  suitable  for  steel-making. 

In  the  Acheson  furnaces,  the  resistor  consists  of  a  special 
core  of  carbon,  surrounded  by  the  charge,  or  the  charge  itself  is 
the  resistor.  In  either  case,  the  resistor  remains  solid  during  the 
operation,  and  cannot  be  lengthened  or  shortened  in  order  to 
regulate  the  current.  Moreover,  as  the  furnace  is  intermittent  in 
action,  the  temperature  of  the  resistor  is  not  constant,  as  in  a 
smelting  furnace,  but  rises  continuously  during  the  run.  This 
rise  of  temperature  reduces  very  considerably  the  resistance  of  the 
furnace,  and  hence, the  relation  between  the  volts  and  the  amperes. 


CONSTRUCTION    AND    DESIGN.  73 

For  example,  supposing  the  furnace  had  a  core  of  coke,  the  re- 
sistance would  fall  to  about  one-half  its  original  value  when  the 
furnace  became  thoroughly  hot,  and  if  the  heat  were  sufficient 
to  graphitize  the  coke,  the  resistance  would  fall  still  further,  the 
resistance  of  the  heated  graphite  being  only  about  ^s  of  that  of 
the  cold  coke  from  which  it  was  originally  produced.  Such  a 
furnace  would  be  very  difficult  to  operate  with  a  constant  voltage 
supply ;  because  if  it  were  proportioned  so  as  to  draw  a  suitable 
current  when  heated,  the  current  that  would  flow  through  the  cold 
furnace  would  be  so  small  (only  ^  of  the  final  current),  that  the 
furnace  would  heat  up  very  slowly,  and  the  consumption  of  power 
would  change  very  considerably  during  the  run.  The  price  paid 
for  electrical  energy  is  usually  based  upon  the  maximum  rate  at 
which  it  will  be  used,  and  a  furnace  which  only  used  15  to  25  per 
cent,  of  its  maximum  power  for  a  large  proportion  of  the  run, 
would  be  very  inefficient  financially.  It  is  necessary,  therefore, 
to  change  the  voltage  of  the  supply  during  the  run,  and  for  this 
purpose  a  special  induction  regulator  has  been  devised,  which  will 
change  the  voltage  from  about  200  volts  at  the  beginning  of  the 
run  to  80  volts  at  the  end  of  the  run,  maintaining  the  same  power 
(about  1,000  H.P.)  all  the  time.* 

It  will  be  noticed  that  the  change  in  the  voltage  is  less  than 
the  change  in  the  resistance  of  the  furnace.  This  follows  directly 
from  the  relationship  between  volts,  amperes,  and  watts,  because 
(omitting  any  consideration  of  inductance),  the  voltage  must  vary, 
for  constant  power,  as  the  square  root  of  the  resistance  of  the 
furnace.  Thus,  if  P  is  the  power  in  watts,  E  the  voltage,  C  the 
current  in  amperes,  and  R  the  resistance  in  ohms  :— 

E  E1 

P  =  EC,     and    C=      — ,  therefore   P  = 

.       R  R 

or,  for  constant  power,  E  must  vary  as  the  square  root  of  R. 

Resistors. t 

The  materials  employed  as  resistors  determine  very,  largely 
the  voltage  of  electric  furnaces,  and  have  been  referred  to  under 

*F.  A.  J.  FitzGerald,  Miscellaneous  Accessories  of  Resistance  Furnaces, 
Flectrochem.  Industry,  vol.  in.,  p.  n. 

•f-This  convenient  term  for  "a  substance  used  because  of  its  property  of  offering 
resistance  to  the  passage  of  an  electric  current,"  was  suggested  by  F.  A.  J.  Fitz- 
Gerald, Electrochemical  Industry,  vol.  ii.,  p.  490,  to  avoid  attaching  two  meanings  to 
the  word  "resistance." 


74  THE     ELECTRIC     FURNACE. 

that  heading ;  but  it  will  be  convenient  to  consider  them  particu- 
larly at  this  point. 

Three  cases  present  themselves:  (i)  Arc  furnaces — in  which 
the  resistor  consists  of  the  intensely  heated  gases  and  vapours  in 
the  arc.  (2)  Furnaces  having  a  special  resisting  core,  in  which 
the  heat  is  developed.  (3)  Furnaces  in  which  the  current  passes 
through,  and  directly  heats,  the  charge  itself. 

The  arc  furnaces  need  not  be  specially  considered,  as  any 
gases  or  vapours  that  are  ordinarily  present  in  electric  furnaces, 
will  serve  to  carry  the  current.  More  furnaces  belong  to  class 
(3)  than  to  class  (2) ;  and  it  will  obviously  be  more  satisfactory, 
when  possible,  to  pass  the  current  through  the  material  of  the 
charge,  instead  of  providing  a  special  resistor  for  this  purpose. 
The  electrical  conductivity  of  the  charge  will  usually  determine 
whether  it  can  be  used  as  a  resistor.  Of  the  ordinary  materials 
found  in  nature,  only  the  metals  and  carbon  are  sufficiently  con- 
ductive to  carry  large  electrical  currents ;  but,  when  heated  to 
their  melting  temperature,  most  of  the  rock-forming  minerals  will 
carry  an  electric  current ;  and  when  mixed  in  suitable  proportions 
for  a  melting  charge,  and  fused,  they  always  form  sufficiently  good 
electrical  conductors. 

The  conductivity  of  molten  slags,  enables  continuous  smelt- 
ing furnaces  to  be  operated  electrically,  although  the  ore  fed  into 
the  furnace  may  be  non-conducting.  The  furnace  may  be  started 
in  the  first  place  by  means  of  an  arc  between  the  electrodes ;  the 
heat  of  the  arc  melting  some  of  the  surrounding  material,  which 
ultimately  fills  the  space  between  the  electrodes  with  a  molten  con- 
ducting slag.  Heat  is  then  generated  by  the  passage  of  the  cur- 
rent through  the  slag,  more  ore  becomes  heated  and  melted,  and 
after  a  time  the  whole  crucible  of  the  furnace  becomes  thoroughly 
heated  and  filled  with  molten  slag  and  metal.  Another  way  of 
starting  such  a  furnace  is  by  placing  some  coke  between  the 
electrodes.  The  coke,  being  a  moderately  good  conductor,  soon 
becomes  heated  by  the  passage  of  the  current,  and  melts  the  sur- 
rounding ore  charge.  The  electrodes  are  then  pulled  further 
apart  and  the  operation  goes  on  as  described  above.  A  third 
method  consists  in  pouring  into  the  furnace  a  potful  of  molten 
slag,  when  the  current  may  be  at  once  switched  on,  and  the 
furnace  will  soon  be  in  regular  operation. 

Although  the  ordinary  rocks  and  ore  minerals  are  very  poor 
electrical  conductors,  when  cold,  the  coke,  which  is  often  added 
to  the  charge  as  a  reducing  reagent,  is  a  fair  conductor,  and,  if 


CONSTRUCTION    AND    DESIGN.  75 

present  in  sufficient  quantity,  will  render  the  charge  somewhat 
conducting. 

Elctrical  Resistivity. — In  order  to  design  a  furnace  that  will 
carry  a  certain  electrical  current  at  a  given  voltage,  it  is  necessary 
to  know  the  numerical  value  of  the  electrical  resistivity  of  the  ma- 
terials through  which  the  current  will  pass  in  the  furnace.  The 
Resistivity,  or  Specific  Resistance  of  a  substance,  is  the  resistance, 
in  ohms,  between  two  opposite  faces  of  a  unit  cube  of  the  material. 
A  cube  of  one  centimeter  edge  is  usually  referred  to,  but  it  is 
sometimes  more  convenient  to  know  the  resistance  of  an  inch 
cube.  If  the  resistivity,  or  resistance  of  an  inch  cube  of  a  sub- 
stance, were  R  ohms,  the  resistance,  between  the  ends  of  a 
cylinder  of  this  material,  L  inches  long,  and  C  square  inches  in 

L 
cross   section,    would   be  be   R — .      The  electrical   resistance,    in 

C 

ohms,  of  any  conductor,  shows  the  voltage  that  would  he  needed 
to  maintain  a  steady  current  of  one  ampere,  through  the  con- 
ductor. Electrical  conductivity  is  the  inverse  of  resistivity,  and 
shows  the  number  of  amperes  that  would  flow  through  a  unit  cube 
if  an  electrical  pressure,  or  electro-motive  force  of  one  volt,  were 
maintained  between  two  opposite  faces  of  the  cube.  The  unit 
of  electrical  conductance  is  the  Mho;  that  is,  ohm  written  the 
wrong  way  round. 

Furnaces  having  Special  Resisting  Cores. — The  cores  or  re- 
sistors in  such  furnaces  are  usually  composed  of  carbon,  which,  in 
the  form  of  coke  powder,  for  example,  is  of  moderate  conductivity, 
thus  allowing  large  currents  to  flow,  and  at  the  same  time  having 
a  sufficient  electrical  resistivity  to  allow  fairly  high  voltages  to 
be  employed — even  when  the  cores  are  of  considerable  cross  sec- 
tion and  moderate  length.  The  resistivity  of  powdered  carbon 
depends  upon  the  fineness  of  grain,  as  well  as  upon  the  resistivity 
of  the  solid  material  from  which  the  powder  was  produced.  In 
order  to  obtain  uniform  heating,  it  is  advisable  to  sort  the  powder, 
only  using  particles  that  are  of  a  uniform  size ;  under  such  con- 
ditions the  resistivity  increases  with  the  fineness  of  the  powder. 
The  following  resistivities  for  graphitized  coke  powder  have  been 
calculated  from  experiments  by  FitzGerald.*  The  resistivity  of 
ordinary  coke  powder  would  probably  be  about  four  times  as 
large. 


'Francis  A.  T.  FitzGerald.     Electrochemical  Industry,  vol.  ii.,  (1904),  p.  490. 


76  THE    ELECTRIC     FURNACE. 

TABLE  VIII. 
Resistivity  of  Graphitized  Coke  Powder. 

(Ohms  for  one  cubic  inch). 

Red  hot 

Size  of  Grains.  Cold.  Red  hot.   &  weighted. 

Between  5  meshes  and  6  meshes 

to  the  inch      0-36  0.24  0.15 

Between  3  meshes  and  4  meshes 

to  the  inch      0.29  0.19  o.n 

The  first  powder  had  been  passed  through  a  sieve  having  5  meshes 
to  the  linear  inch,  and  had  been  passed  over  a  sieve  of  6  meshes 
to  the  inch.  The  second  powder  had  been  passed  through  a  3 
mesh  sieve  and  over  a  4  mesh  sieve.  The  restivities  are  given 
for  the  cold  powder,  and  at  a  red  heat.  The  third  column  shows 
the  resistivity  of  the  red  hot  powder  when  a  weight  wras  laid 
upon  it,  thus  making  a  better  electrical  contact  between  the 
adjacent  grains.  The  powder  was  placed  in  an  open  trough,  and 
was  only  four  inches  in  depth  ;  it  would,  therefore,  be  more  lightly 
packed  than  in  the  core  of  a  full-sized  furnace.  The  figures  in 
the  last  column  would  consequently  more  nearly  represent  regular 
furnace  conditions.  The  figures  are  given  for  one  cubic  inch, 
as  inches  are  still  more  frequently  used,  in  this  country,  than 
centimeters;  to  convert  to  centimeter  resistivities,  multiply  by 
2.54 — the  number  of  centimeters  in  one  inch. 

For  many  purposes  ordinary  coke  powder  would  form  a  bet- 
ter resistor  than  the  graphitized  material,  on  account  of  its  higher 
resistivity;  but  it  has  this  serious  disadvantage,  that  if  very 
strongly  heated  in  the  furnace  the  coke  will  become  graphitized, 
and  its  resistivity  will  fall  to  about  a  quarter  of  its  original  value 
for  corresponding  temperatures.  It  will  consequently  be  better, 
in  high  temperature  furnaces,  to  use  a  core  that  has  previously 
been  graphitized,  thus  obtaining  a  more  nearly  constant  material 
for  the  resistor. 

Solid  rods  of  carbon  (amorphous  or  graphitized)  are  some- 
times used  as  resistors,  as  in  Borchers'  resistance  furnace,  (Fig. 
14,  page  24),  or  in  Acheson's  siloxicon  furnace,  (Fig.  41,  page 
154).  The  resistivity  of  rods  of  carbon,  such  as  are  used  for 
electric  lighting  and  furnace  electrodes,  and  of  the  graphitized 
electrodes,  is  very  much  less  than  that  of  the  same  material  in 
the  form  of  a  powder.  The  following  are  approximate  values  : — 


CONSTRUCTION    AND    DESIGN.  77 

TABLE  IX. 
Resistivity  of  Solid  Carbon. 

(Ohms  for  one  cubic  inch). 

Cold.  Hot. 

Amorphous        00124 — .00163  .0006 — .0008 

Graphitic       00032 — .00042  .00016 — .0002 

In  this  table,  "amorphous"  refers  to  the  ordinary  carbon  electrode, 
or  arc  light  carbon;  while  "graphitic"  refers  to  the  graphitized 
electrodes.  The  word  "hot"  refers  to  electric  furnace 
temperatures,  such  as  2,ooo°C.,  or  3,ooo°C.,  and  it  will  be  obvious 
that  only.approximate  values  can  be  given. 

The  smaller  values  under  the  heading  "cold"  were  determined 
by  Mr.  P.  M.  Lincoln,  of  the  Niagara  Falls  Power  Co.,  on  rods 
of  about  1.6  square  inches  cross  section,  and  about  12  inches 
long.  They  are  published  by  the  Acheson  Graphite  Company  in 
their  pamphlet  on  Acheson  Graphite  Electrodes.  The  larger 
values  are  taken  from  a  paper  by  Messrs.  FitzGerald  and  Forssell 
and  represent  a  large  number  of  experiments  on  electrodes  of 
4x4  inches  section,  and  from  40  inches  to  93  inches  in  length. 
The  values  under  the  heading  "hot"  do  not  represent  actual  ex- 
periments, but  depend  on  the  assumption  that  at  furnace 
temperatures  the  resistivity  of  carbon  is  one-half  of  its  resistivity 
when  cold.  Mr.  Francis  F.  J.  FitzGerald  has  kindly  furnished 
the  author  (before  publication),  with  the  results  of  his  experi- 
ments,* from  which  the  following  table  has  been  summarized. 
Unfortunately  the  experiments  were  not  continued  to  sufficiently 
high  temperatures  to  give  much  information  about  the  resistivity 
at  electric  furnace  temperatures,  but  as  far  as  they  go  they  indi- 
cate a  more  rapid  decrease  of  resistivity  with  temperature  in  the 
graphite  than  in  the  amorphous  carbon.  The  experiments 
were  made  at  the  works  of  the  National  Carbon  Com- 
pany. 

The  results  quoted  are  from  an  amorphous  carbon  electrode, 
4x4  inches  section  and  73  inches  long,  and  from  an  Acheson 
graphitized  electrode  4x4  inches  section  and  40  inches 
long. 


'FitzGerald   and  Forssell,   Trans.   Amer.    Electrochera.    Soc.,  vol.   xi. 


THE     ELECTRIC     FURNACE. 

TABLE  X. 
Resistivity  of  Amorphous  and  Graphitic  Carbon. 

Experiments  by  FitzGerald  and  Forssell. 

Resistivity,  ohms  for  i  inch  cube. 
Temperature.  Amorphous.  Graphitic. 

io°C.  .00163  .000416 

6i°C.  .00160  .000387 

io9°C.  .000356 

i85°C.  -000338 


282°C.  .00158 

390°C.  -00153 

466°C.  .00150 


Furnaces  in  which  the  Current  Passes  through  the  Charge. — 

The  writer  has  attempted  to  calculate  the  resistivity  of  the  melt- 
ing materials  in  the  fusion  zones  of  the  Heroult  and  Keller  ore- 
smelting  furnaces,  and  also  of  molten  slags  themselves.  The 
data  available  were  very  unsatisfactory,  and  the  results  obtained 
can  only  be  taken  as  representing  in  the  roughest  way  the  re- 
sistivities of  these  materials.  The  Heroult  and  Keller  smelting 
zones  appear  to  have  a  resistivity  of  about  o.  i  ohm  for  one  cubic 
inch,  varying  perhaps  from  about  0.05  to  0.15  ohm.*  The 
resistivity  of  molten  slag  is  less  than  this,  being  in  the  order  of 
o.oi  to  0.05  ohm  for  one  cubic  inch.t  In  the  Gin  and  Kjellin 
steel  furnaces,  the  resistivity  of  molten  iron  is  an  important  factor ; 
and  this  is  very  small,  being  about  0.00007  ohm  for  one  cubic 
inch.t 

With   very    few  exceptions,    the    electrodes,    which    serve   to 
lead  the  electric  current  into  the  furnace,  are  composed  of  carbon. 


"•Calculated  from  the  published  drawings  and  electrical  measurements  for  these 
furnaces,  assuming  that  the  resistivity  is  uniform  throughout  the  volume  between  the 
bottom  of  the  electrode  and  the  surface  of  the  melted  charge. 

fThe  resistivity  of  fused  salts  is  of  about  this  order,  see  J.  W.  Richards,  Con- 
duction in  fused  and  solid  electrolytes.  Trans.  Amer.  Klectrochem.  Soc.,  vol.  vii., 
P  71- 

fG.  Gin  (Ilaanel's  European  Report,  1904,  p.  172),  gives  the  resistivity  of  molten 
pig-iron  as  216x10-'  per  centimeter  cube  (  =  .000,085  ohm  per  inch  cube).  He  has  also 
measured  the  resistivity  of  molten  pig-iron  at  i,3oo°C.  (Trans.  Electrochem.  Soc., 
vol.  viii.,  p.  289),  and  finds  it  to  be  16  x  io-5  (  =  .000,063  ohm  per  inch  cube). 


CONSTRUCTION    AND    DESIGN.  79 

Electrodes. 

They  are  made  from  retort  carbon,  petroleum  coke  and  coal  tar; 
the  pulverized  carbon  being  mixed  with  tar  and  pressed  through  a 
die  of  the  required  shape  and  size.  The  electrodes  are  then  sub- 
jected to  a  baking  process,  which  drives  off  the  volatile  part  of  the 
tar,  and  leaves  a  hard,  compact  mass  of  carbon.  Graphitized 
electrodes  are  made  in  like  manner  from  petroleum,  coke,  and 
tar,  with  the  addition  of  i  %%  or  2%  of  haematite ;  being  heated 
in  an  Acheson  furnace  to  a  very  high  temperature.  The  iron 
which  is  contained  in  the  haematite,  effects  the  conversion  of  the 
carbon  into  graphite,  and  is  finally  expelled,  by  volatilization,  at 
the  extremely  high  temperature  of  the  furnace ;  leaving  the 
electrodes  composed  of  compact  graphite.  Molten  iron  has  the 
property  of  dissolving  carbon,  which  separates  from  the  iron  as 
graphite  on  cooling ;  but  it  is  difficult  to  understand  how  so  small 
a  proportion  of  iron  can  change  the  whole  electrode  into  graphite. 

Graphitized  electrodes  have  the  advantage  of  purity,  good 
conductivity,  and  great  resistance  to  oxidation. 

Their  purity  renders  them  very  advantageous  in  operations 
like  the  production  of  aluminium,  in  which  the  electrode  ash  enters 
the  electrolyte,  and  contaminates  the  resulting  metal.  The  char- 
acteristic resistance  of  these  electrodes  to  oxidation,  reduces  their 
consumption,  and  their  good  conductivity  has  a  similar  effect, 
since  smaller  electrodes  can  be  employed.  Graphitized  electrodes 
are  largely  used  for  electrolysis,  but,  in  electric  smelting  furnaces, 
cheaper  ones  made  of  coke  and  tar  have  usually  been  employed ; 
while  in  some  cases  the  coke  forming  part  of  the  furnace  charge 
has  been  utilized  for  leading  in  the  current ;  electrical  contact  be- 
ing made  through  the  charging  hoppers.  The  kind  of  electrode 
to  be  employed  will  depend  largely  upon  the  oxidizing  or  reducing 
character  of  the  furnace.  In  the  former  case  the  graphitized 
electrodes  would  be  preferable,  while  in  the  latter,  the  ordinary 
kind  would  serve  the  purpose. 

Approximate  figures,  for  the  resistivity  of  carbon  and 
graphite  electrodes,  have  already  been  given.  By  means  of  these, 
it  is  easy  to  calculate  the  drop  of  voltage  that  would  be  produced 
in  electrodes  of  a  certain  length  and  cross  section,  by  any 
particular  current.  The  cross  section  of  an  electrode  is  usually 
determined  by  the  amount  of  current  to  be  carried.  The  current 
density  or  the  number  of  amperes  per  square  inch  of  cross  section 
of  the  electrode,  differs  considerably  in  different  types  of  furnaces 
and  for  different  kinds  of  electrodes,  being  much  higher  in 


80  THE     ELECTRIC     FURNACE. 

graphitized  electrodes  than  in  the  ordinary  variety.  The  large 
electrodes  used  in  the  Heroult  and  Keller  furnaces  carry  about 
20  amperes  per  square  inch,  while  small  round  electrodes  and 
graphite  electrodes  carry  more,  up  to  about  100  amperes  per 
square  inch.  Moissan  used  currents  up  to  200  or  even  700 
amperes  per  square  inch,  in  small,  ungraphitized  electrodes,  but 
this  would  be  far  too  high  for  commercial  work,  as  the  carbons 
would  become  red  hot  and  would  rapidly  waste  away,  and  the 
consumption  of  electrical  energy,  in  the  electrode,  would  be  too 
high  to  be  tolerated.  The  loss  by  oxidation,  of  the  exposed  part 
of  an  electrode,  can  sometimes  be  prevented  by  a  system  of  water 
jackets,  as  in  the  Heroult  steel  furnace,  Fig.  23.* 

The  only  furnaces  in  which  some  form  of  carbon  electrode  is 
not  employed,  are  the  electrodeless  furnaces,  such  as  the  Kjellin 
furnace,  and  furnaces  in  which  metallic  electrodes,  usually  water 
cooled,  are  employed,  such  as  the  Gin  steel  furnace,  the  Laval  ore- 
smelting  furnace,  and  Borchers'  aluminium  furnace. 

Electrode  holders  are  employed  for  making  electrical  connec- 
tion between  the  electrode  and  the  cable  which  supplies  the  electric 
current.  They  are  also  used  for  supporting  and  manipulating 
movable  electrodes.  The  holders  are  made  of  copper  or  bronze, 
which  are  preferable  on  account  of  their  good  electrical  conduc- 
tivity, or  of  iron  or  steel,  which  are  cheaper  and  do  not  melt  so 
easily  if  over-heated.  It  is  not  easy  to  maintain  a  thoroughly 
good  electrical  contact  between  the  holder  and  the  carbon 
electrode,  because  the  electrodes  and  their  holders  become  heated, 
and  the  expansion  of  the  metal  loosens  its  hold  on  the  carbon. 
The  relatively  poor  conductivity  of  carbon  makes  a  large  area  of 
perfect  contact  desirable,  while  its  small  mechanical  strength 
renders  it  difficult  to  clamp  the  holder  sufficiently  tightly  without 
breaking  the  electrode.  In  addition  to  this,  the  heat  of  the 
furnace  tends  to  render  unworkable  any  bolts  and  nuts  or  similar 
mechanical  devices. 

Graphitized  electrodes  can  be  easily  machined  or  threaded, 
and  attached  in  this  way  to  the  holder;  but  for  electric  smelting 
furnaces,  electrodes  of  rectangular  cross  section  are  more  usually 
employed,  and  these  are  secured  in  their  holders  by  bolting  or 
clamping.  The  electrodes,  in  smelting  furnaces,  are  usually 

*F.    M.    Becket    proposes    to    pre%-ent    the    oxidation    and    destruction  of    carbon    or 

graphite    electrodes,     by    surrounding     them     with     water-cooled     jackets  at    the    point 

where   they   enter  the    furnace.      U.S.    patent   855,441,    see   Electrochemical  Industry,  vol. 
v.,  p.    279. 


CONSTRUCTION    AND    DESIGN. 


8l 


vertical,  in  order  to  be  more  easily  manipulated,  and  are  suspended 
by  a  chain,  so  as  to  be  easily  raised  or  lowered ;  the  electric  cable 
being  attached  directly  to  the  electrode  holder.  The  holder  used 
in  the  Heroult  ore-smelting  furnace,  Fig.  29,*  may  be  taken  as 
an  example.  The  part  A  is  made  of  steel,  and  the  descending 
jaws  JJ  fit  into  the  sides  of  the  electrode  and  are  prevented  from 
spreading  by  the  two  bolts.  The  electrode  is  driven  downward 
by  wedges,  thus  making  good  contact  with  the  jaws.  The  upper 
part  B  is  made  of  sheet  copper,  and  enables  the  electric  cable,  and 
the  pulley  and  chain  by  which  the  electrode  is  suspended,  to  be 
placed  so  far  above  the  furnace,  that  they  will  not  be  over-heated, 
while  the  lower  part  A  can  be  cooled  by  air  or  water  introduced 
from  above.  The  electrodes  of  the  Heroult  steel  furnacet  are 
supported  by  arms  from  the  back  of  the  furnace,  instead  of  by 
chains ;  this  construction  being  better  adapted  to  a  tilting  furnace. 
The  electrode  is  square  in  section,  and  is  surrounded  by  four  con- 
tact pieces,  one  for  each  side.  One  of  these  pieces  is  attached 
to  the  arm  and  the  other  three  are  tightened  against  the  electrode 
by  a  steel  strap,  which  encircles  them,  and  is  drawn  tight  by  a 
screw  contained  within  the  arm. 


Fig.  22.— Electrode  Holder  of  Heroult  Steel  Furnace. 

The  holder  is  shown  in  outline  in  Fig.  22.  A  A  is  the  arm 
with  tightening  screw,  S  and  nut  N,  to  which  is  attached  the  strap 
F,  which  draws  the  contact  pieces  B,  C  and  D  against  the  electrode 
E,  and  the  latter  against  the  arm  A.  A  cable,  not  shown  in  the 
sketch,  is  bolted  to  A,  B,  C,  and  D,  thus  distributing  the  current 
to  the  movable  electrodes.  A  shield  is  provided  to  protect  the 
holder  from  the  heat  and  smoke  of  the  furnace. 


*Dr.  Haanel,  Report  on  Experiments  at  Sault  Ste.   Marie,  1907,  plate  vii. 
fDr.   Haanel,   European    Report,    1904,    Figs.    3-7. 


82  THE    ELECTRIC     FURNACE. 

Measurement  of  Furnace  Temperatures. 

In  many  furnace  operations  it  is  very  important  to  be  able  to 
measure  the  temperature  attained,  and  pyrometry,  or  the  measure- 
ment of  high  temperatures,  has  developed  rapidly  during  recent 
years. 

For  the  measurement  of  ordinary  or  fuel-fired  furnaces  many 
satisfactory  instruments  exist, *  among  which  may  be  mentioned  ; 
the  Seger  cones,  the  electrical  pryometers  such  as  the  Callendar 
resistance  pyrometer,  and  the  thermo-electric  pyrometer,  and 
various  optical  pyrometers.  The  Seger  conest  are  a  series  of 
small  pyramids,  consisting  of  clay  and  other  materials,  carefully 
proportioned  so  that  each  has  a  definite  melting  temperature.  By 
placing  several  of  these  in  a  furnace  and  noting  which  of  them 
are  melted  during  the  operation,  it  is  possible  to  state  approxi- 
mately what  temperature  was  attained.  The  Callendar  resist- 
ance pyrometer!  contains  a  coil  of  platinum  wire  carefully  in- 
sulated and  protected  from  the  furnace  gases,  and  so  arranged 
that  its  electrical  resistance  can  be  accurately  measured.  The 
resistivity  of  pure  metals  increases  very  regularly  with  the 
temperature,  and  accurate  temperature  measurements  can  be  made 
in  this  manner  up  to  i,ooo°C.,  or  i,ioo°C.  The  thermo-electric 
pyrometer§  consists  of  two  wires  of  different  metals.  These  are 
fused  or  twisted  together  at  one  end  which  is  placed  in  the  furnace, 
while  the  other  ends  of  the  wires  are  connected  to  a  galvanometer 
or  instrument  for  measuring  a  very  small  electric  current.  When 
the  junction  of  the  wires  is  heated,  a  small  electric  current  is 
generated  and  in  this  way  the  temperature  of  the  furnace  can  be 
measured.  The  indications  of  this  instrument  are  somewhat  less 
accurate  than  those  of  the  platinum  resistance  pyrometer,  but  the 
thermocouple  can  be  used  up  to  i,7oo°C.,  and  in  many  ways  is 
more  convenient  than  the  resistance  pyrometer.  For  very  high 
temperatures  the  wires  are  composed  of  platinum  and  an  alloy  of 

""'High-temperature  Measurements,"  by  Le  Chatelier  and  Boudouard,  trans,  by 
C.  K.  Burgess. 

Pyrometers    suitable    for    Metallurgical  Work.     Journ.    Iron    and    Steel  Inst.    I.,   1904. 

Methods  of  Pyrometry,  C.  L.  Waidner,  Proc.   Eng.   Soc.   of  Western  Pa.,  1904,  p.  98. 

fSeger  Cones,  Le  Chatelier  and  Boudouard,  p.  170.  Hofman  and  Demond.  Trans. 
Amer.  Inst.  of  Mining  Engineers,  vol.  xxiv. ,  p.  42,  and  xxix.,  p.  682. 

^Technical  Thermometry,  a  pamphlet  issued  by  the  Cambridge  Scientific  Instru- 
ment Co.,  1906. 

Callendar,    Phil.    Mag.,    vol.    xlvii.,    1899,    PP-    191    and    519. 

Chappuis   and  Harker,   Phil.    Trans.    Roy.    Soc.   A.,   vol.    194,    1900,    pp.    37-134. 

§Barus.   Bull,  U.S.  Geol.   Survey,  No.  54,  Washington,   1889. 

Roberts-Austen,     Trans.    Amer.     Inst.     of     Mining     Engineers,     1893. 

Stansfield,   Phil.    Mag.,   xlvi.,   1898,   p.   59. 


CONSTRUCTION    AND    DESIGN.  83 

platinum  with  rhodium  or  iridium,  but  for  lower  temperatures 
cheaper  metals  can  be  used  as  in  the  Bristol  electric  pyrometers.* 
Optical  or  radiation  pyrometers  depend  on  the  measurement  of 
the  amount  or  the  color  of  the  light  emitted  by  a  heated  substance, 
or  of  the  amount  of  heat  which  is  radiated,  t 

Far  greater  difficulties  are  met  with  in  attempting  to  measure 
the  temperatures  of  electric  furnaces  and  comparatively  little  ad- 
vance has  been  made  in  this  direction.  The  optical  pyrometers 
are  suitable  for  this  purpose,  because,  being  used  from  outside 
the  furnace,  their  use  is  not  limited,  like  that  of  other  pyrometers, 
by  the  melting  of  the  instrument  itself  when  used  to  measure  a 
very  high  temperature.  Some  careful  measurements  in  an  electric 
tube  furnace  have  been  made  by  Messrs.  Tucker  and  Lampen  by 
means  of  a  Wanner  optical  pyrometer.  J  Other  methods  of 
measuring  electric  furnace  temperatures  consist  in  placing  in  the 
furnace  a  piece  of  carbon  or  of  some  other  refractory  material 
and  noting  at  the  end  of  the  operation  what  change  has  taken 
place  in  the  material  used.§  In  the  case  of  carbon  the  specific 
gravity  increases  with  the  temperature  to  which  it  has  been  ex- 
posed, but  the  change  depends  upon  the  time  during  which  it  has 
been  heated  as  well  as  upon  the  highest  temperature  attained,  and 
the  indications  of  such  a  test  are  difficult  to  convert  into  degrees 
of  temperature.  In  some  cases  the  temperature  of  an  electric 
furnace  can  be  determined  from  the  amount  of  electrical  energy 
supplied  to  it.  Thus  Mr.  W.  C.  Arsem,  in  working  with  a  small 
vacuum  electric  furnace,  observed  how  much  power  was  needed 
to  maintain  the  furnace  at  three  lower  temperatures,  which  could 
be  measured,  and  then  deduced  by  means  of  a  curve  the 
temperature  that  should  be  produced  by  any  other  amount  of 
electric  power.  I! 

Conclusion. 

A  chapter  on  "Electric  Furnace  Design,  Construction  and 
Operation"  would  include,  if  the  subject  were  fully  treated,  a  vast 


*W.  H.  Bristol,  45  Vesey  St.,  New  York.  See  Electrochemical  Industry,  vol.  iv., 
p  115,  and  F.  F.  Schuetz.  A  thermo-electric  pyrometer  for  general  industrial  applica- 
tions, Trans.  Amer.  Electrochem.  Soc.,  vol.  x.,  p.  81. 

•{•Optical  Pyrometry,  by  C.  W.  Waidner  and  G.  K.  Burgess.  Bull.  No.  2,  Bureau  of 
Standards,  Washington,  1905. 

tS.  A.  Tucker  and  A.  Lampen,  Journ.  Amer.  Chem.  Soc.,  vol.,  xxviii.,  pp.  846  and 
853.  Trans.  Amer.  Electrochem.  Soc.,  vol.  xi.,  and  Electrochemical  Industry,  vol.  v., 
p.  227. 

§F.   A.    J.   FitzGerald.      Trans.    Amer.    Electrochem.    Soc.,   vol.    vi.,    p.    31. 

||W.  C.  Arsem,  The  Electric  Vacuum  Furnace.  Trans.  Amer.  Electrochem.  Soc., 
•vol.  ix.,  p.  153. 


84  THE     ELECTRIC     FURNACE. 

amount  of  very  varied  information.  Certain  branches,  such  as 
the  details  of  electrical  measurement  and  construction  have  been 
omitted,  as  being  too  large  for  inclusion,  and  as  having  been  fully 
treated  in  standard  works.  Reference  should  be  made  to  the 
following  papers  on  Electric  Furnace  Design  by  Francis  A.  ]. 
FitzGerald,  and  by  C.  L.  Collens : — 

F.  A.  J.  FitzCerald. — Note  on  Some  Theoretical  Considerations  in 
the  Construction  of  Resistance  Furnaces.  Tran.  Amer.  Electrochem. 
Industry,  vol.  iv.,  p.  9.  Some  first  principles  of  Electrical  Resistance 
Furnaces,  Electrochem.  Industry,  vol.  ii.,  p.  342.  Miscellaneous  Ac- 
cessories of  Resistance  Furnaces,  vol.  iii.,  p.  9.  Resistance  Furnace 
for  Crucibles,  p.  55.  Experiments  with  an  Electro-Thermic  Muffle 
Furnace,  p.  135.  The  Borchers'  Furnace,  p.  215.  The  Ruthenburg- 
and  Acheson  Furnaces,  p.  416.  The  Carborundum  Furnace,  vol.  iv., 
P-  53- 

C.  L.  Collens. — Some  Principles  of  the  Resistor  Furnace  Desig'n. 
Trans.  Amer.  Electrochem.  Soc.,  vol.  ix.,  p.  31. 


IRON     AND     STEEL.  85 

CHAPTER  V. 

PRODUCTION  OF  IRON  AND  STEEL  IN  THE 
ELECTRIC  FURNACE. 

Iron  is  employed  in  the  mechanic  arts  in  combination  with 
variable  amounts  of  carbon  and  other  metalloids  and  metals,  as 
wrought  iron,  cast  iron,  or  steel.  These  terms  cover  a  wide  range 
of  different  materials.* 

Cast  iron,  or  pig  iron,  is  the  form  in  which  the  metal  is  usually 
obtained  from  the  ore;  it  contains  from  2%  to  4^2%  of  carbon, 
from  Y-2.%  to  4%  of  silicon,  and  small  but  variable  amounts  of 
manganese,  sulphur  and  phosphorus ;  the  remainder  being  iron. 
The  carbon  and  other  elements  are  absorbed  by  the  iron  during 
its  production  in  the  blast-furnace,  and  make  it  more  easily  fusible 
than  if  it  were  pure ;  the  melting  temperature  of  pure  iron  being 
i5O5°C.,  or  274O°F.,  while  that  of  cast  iron  varies  from  about 
iO27°C.  to  i275°C. ,  or  from  i88o°F.  to  2327*^.,  depending  upon 
its  composition.  The  fusibility  of  cast  iron  makes  it  suitable  for 
use  in  the  foundry,  but  the  presence  of  a  large  amount  of  carbon 
and  other  metalloids  renders  it  far  less  valuable  mechanically  than 
the  purer  forms  of  wrought  iron  and  steel. 

Wrought  iron  consists  of  nearly  pure  iron,  retaining  only 
small  amounts  of  carbon  and  other  metalloids,  together  with  a 
small  amount  of  admixed  slag.  It  is  made  by  melting  pig  iron  in 
the  "puddling"  furnace  in  contact  with  a  cinder  or  slag  rich  in 
oxides  of  iron.  The  carbon  and  other  metalloids  in  the  pig 
iron  are  largely  removed  by  reaction  with  this  slag,  and  the 
nearly  pure  iron  forms  in  grains  in  the  furnace,  being  too  infusible 
to  be  melted.  These  grains  of  iron  are  welded  together,  but  still 
retain  some  of  the  slag  from  the  furnace.  The  puddled  iron,  after 
being  rolled  into  bars,  is  cut  into  short  pieces  which  are  made 
into  bundles  or  "piles,"  which  are  reheated  and  rolled  into  bars  or 
other  shapes.  The  operation  of  "piling"  removes  some  of  the  slag, 
and  improves  the  quality  of  the  iron.  A  large  amount  of  so-called 
wrought  iron  is  made  by  piling  pieces  of  mild  steel. 

Steel  is  a  very  comprehensive  term,  and  includes : — 

(a)  Crucible  Steel,  which  is  made  from  carefully  selected 
varieties  of  wrought  iron  or  steel,  has  been  melted  in  crucibles, 
and  contains  from  about  3^%  to  1^2%  of  carbon,  together  with 
enough  manganese  and  silicon  to  produce  a  sound  casting. 

*The   different   varieties   of   iron    and    steel  have  been  denned   by   the   International 
Association  for  Testing  Materials.     Journ     Iron   and  Steel   Inst.,   1907,    I. 


86  THE     ELECTRIC     FURNACE. 

(b)  Bessemer  and  Open-hearth  Steels  include  all  the 
products  of  these  furnaces,  and  may  range  from  the  hardest  of 
tool  steel  to  a  material  which  is  practically  pure  iron,  and  only 
differs  from  wrought  iron  in  having  been  fused,  and  being  in  con- 
sequence nearly  free  from  slag,  and  in  the  presence  of  a  little 
manganese,  added  to  ensure  a  sound  casting. 

The  production  of  iron  and  steel  in  the  electric  furnace  may 
be  considered  under  three  heads  : — 

I.  The  production  of  steel  by  melting  steel  scrap,  either  alone 
or  with  the   addition  of    pig  iron,   iron  ore,   etc.,   in    an  electric 
furnace. 

II.  The  production   of    pig   iron  by   heating  iron   ore    with 
carbon  and  fluxes  in  an  electric  furnace. 

III.  The  production  of  steel  by  heating  iron  ore  with  carbon 
and  fluxes  in  an  electric  furnace. 

The  first  is  in  commercial  operation,  the  second  is  now  being 
tried  on  a  commercial  scale,  and  will  probably  be  employed  to  a 
limited  extent,  while  the  third  has  been  experimented  with  by 
Stassano  and  others,  but  appears  less  promising  than  the  other 
two. 

I. — Production  of  Steel  From  Scrap,  Pig  Iron  and  Iron  Ore. 

The  furnaces  used  are  electrically  heated  melting  furnaces,  in 
which  the  scrap,  pig  iron,  etc.,  can  be  melted,  and  the  resulting 
steel  can  be  kept  molten  until  its  composition  has  been  adjusted. 
The  metal  is  then  tapped  or  poured  and  cast  into  moulds.  A  steel 
corresponding  to  any  product  of  the  crucible,  Bessemer,  or 
Siemens  furnaces  can  be  produced  in  this  way. 

The  operation  may  be  merely  a  melting  one,  in  which  pure 
steel  scrap  is  melted  and  cast  into  ingots  after  small  additions  of 
pure  pig  iron,  ferro-manganese,  etc.,  or  the  charge  may  consist 
largely  of  pig  iron,  in  which  case  considerable  additions  of  iron 
ore  are  needed  to  remove  excess  of  carbon  and  other  constituents 
of  the  pig  iron.  The  presence  of  phosphorus  or  sulphur  in  steel 
is  objectionable,  and  when  these  are  found  in  more  than  traces  in 
the  charge,  they  must  be  removed  before  the  steel  can  be  cast, 
thus  prolonging  the  operation. 

Three  types  of  electric  furnace  have  been  employed  for  this 
kind  of  steel  making,  the  Heroult  furnace,  Fig.  23,  the  Kjellin 
furnace,  Fig.  24,  and  the  Gin  furnace,  Fig.  28. 

The  Heroult  Steel  Furnace,  Fig.  23,*  resembles  a  Wellman 
tilting,  open-hearth  furnace,  from  which  the  gas  and  air  ports 
have  been  removed,  and  with  the  addition  of  two  vertical  carbon 

*European    Commission    Reporf,    1904,    Fig.    4. 


IRON     AND     STEEL.  87 

electrodes,  CC.  The  furnace  is  heated  by  two  electric  arcs,  one  be- 
tween each  electrode  and  the  slag  or  melted  metal  beneath  it.  The 
current  passes  down  one  electrode,  through  the  metal  and  up  the 
other  electrode. 

The  lining  of  the  furnace  is  constructed  of  dolomite  bricks,  B, 
and  crushed  dolomite,  L.     A  is  the  roof,   and  M  is  the  molten 


Fig.  23.— Heroult  Steel  Furnace. 

steel,  which  is  covered  with  a  layer  of  slag  S,  as  in  the  ordinary 
gas-fired  furnace.  The  furnace  is  built  in  a  steel  case  or  jacket, 
and,  unlike  the  open-hearth  furnace,  the  roof,  A,  is  also  covered 
with  steel  plates,  E,  and  is  provided  with  eyes,  not  shown  in  the 
figure,  by  which  it  may  be  lifted  off  the  furnace.  The  weakest 
part  of  the  roof  is  around  each  electrode,  and  this  part  has  been 
strengthened  by  water  jackets,  J,  which  enable  a  closer  fit  to  be 
maintained  round  the  electrode,  and  so  reduce  the  loss  of  heat  and 
prevent  the  exposed  parts  of  the  electrodes  from  becoming  red 
hot,  and  wasting  in  the  air.  As  an  alternating  current  is  used, 
it  is  not  desirable  to  have  iron  or  steel  plates  on  the  part  of  the 
roof  between  the  electrodes  CC,  as  this  would  increase  the  in- 
ductance of  the  electric  circuit  and  lower  the  power  factor  of  the 
furnace;  bronze  plates,  F,  are  therefore  used  to  cover  this  part  of 
the  roof.  The  charging  doors,  DD,  in  this  furnace  are  placed  at 
the  ends.  The  electrodes  are  square  in  cross  section,  and  are 
vertical  when  the  furnace  is  upright,  but  on  account  of  the  tilting 


88  THE     ELECTRIC     FURNACE. 

motion  of  the  latter,  they  cannot  be  suspended  as  in  the  ore-smelt- 
ing furnaces,  but  are  held  in  adjustable  holders,  Fig.  22,  which 
are  supported  by  the  furnace,  so  that  the  height  of  each  electrode 
in  the  furnace  is  unaffected  by  the  tilting  movement.  The  lower 
end  of  each  is  kept  a  short  distance  above  the  slag,  leaving  a 
space  for  the  electric  arc,  and  the  current  is  regulated  by  raising 
or  lowering  the  electrodes.  This  adjustment  is  effected  by  auto- 
matic machinery  controlled  by  the  voltage  of  the  furnace ;  and  in 
order  that  the  two  arcs  may  be  kept  equal,  each  electrode  is  oper- 
ated separately,  being  controlled  by  the  voltage  between  itself  and 
the  metal  in  the  furnace.  The  hearth  is  lined  with  dolomite  or 
magnesite,  either  of  which  has  the  advantage  of  being  more  re- 
fractory than  silica  brick,  and  of  allowing  strongly  basic  slags  to 
be  used,  for  the  purpose  of  removing  phosphorus  and  sulphur 
from  the  steel. 

The  Heroult  furnace  is  very  much  smaller  than  the  usual 
open-hearth  furnace,  the  one  at  La  Praz  being  about  7  ft.  by  4  ft., 
internally,  and  taking  a  charge  of  only  3  tons,  while  the  furnace 
at  Kortfors  was  a  little  larger  than  this.  For  products  like 
crucible  steel  the  small  size  of  the  electric  furnace  may  be  no 
disadvantage,  but  if  it  is  desired  to  turn  out  structural  or  rail 
steel,  larger  furnaces  will  have  to  be  employed  to  compete  with 
the  5O-ton  open-hearth  furnaces. 

The  Haanel  Commission  saw  the  process  of  making  both  low 
and  high  carbon  steel  in  the  furnace  at  La  Praz,"*  by  melting 
miscellaneous  steel  scrap,  purifying  it  by  repeated  additions  of 
iron  ore  and  lime,  and  then  making  suitable  additions  to  obtain 
the  required  percentage  of  carbon,  manganese  and  silicon.  The 
scrap  contained  0.055%  of  sulphur  and  0.22%  of  phosphorus, 
while  the  final  steel  contained  only  0.02%  of  sulphur  and  0.009% 
of  phosphorus,  the  carbon  being  0.08%  and  1.0%  in  the  two  steels. 
The  scrap  was  melted  with  some  ore  and  lime,  and  when  fusion 
was  complete  the  slag  was  poured  off  and  a  second  slag  was  made 
by  adding  lime  with  a  little  sand  and  fluor  spar  as  fluxes.  The 
second  slag  was  poured  off  and  a  third  slag  made  in  the  same 
way  before  the  final  additions  were  made  to  the  steel.  The  steel 
is  more  completely  purified  in  this  way,  by  the  repeated  addition 
of  fresh  slag-forming  materials,  than  if  the  whole  amount  were 
added  at  once.  In  making  the  low  carbon  steel  some  ferro- 
manganese  was  added  in  the  furnace  and  a  little  aluminium  in  the 
ladle,  while  in  making  the  high  carbon  steel  there  was  also  added 


^European    Commission   Report,   pp.    70-72,    charges   658   and   660. 


IRON     AND     STEEL.  89 

in  the  furnace  some  "carburite,"  which  is  a  mixture  of  iron  and 
carbon,  and  some  ferro-silicon. 

The  electrical  power  employed*  was  about  350  kilowatts  in 
each  operation;  the  voltage  was  no,  and  the  current,  which  was 
not  measured,  would  probably  be  about  4,000  amperes.  The 
electrical  energy  per  ton  of  steel  was  0.17  horse-power  years. t 
The  time  required  was  5  hours  for  a  small  charge  of  i  ^  tons  of 
low  carbon  steel,  and  eight  hours  for  2^/1  tons  of  high  carbon 
steel.  During  the  first  part  of  the  operation  before  the  steel  scrap 
is  melted,  the  current  fluctuates  violently,  and  is  regulated  by 
hand ;  but  after  the  steel  has  melted  around  the  electrodes  the  cur- 
rent becomes  more  steady,  heating  by  an  arc  beneath  each  elec- 
trode, and  automatic  regulation  can  be  employed.  The  full  power 
was  not  applied  until  about  an  hour  after  the  start.  Mr.  Harbord 
states!  that  the  high  carbon  steel  is  as  good  as  corresponding 
grades  of  crucible  steel,  and  there  appears  to  be  no  reason  why,  in 
localities  where  water  power  is  cheap,  this  furnace  should  not  re- 
place the  crucible  furnace  and  open-hearth  furnace  for  the  manu- 
facture of  tool  steels  and  other  special  varieties  of  steels  in  which 
quality  rather  than  quantity  or  cheapness  is  aimed  at. 

More  recent  data  with  regard  to  the  operation  of  the  Heroult 
steel  furnace  are  given  by  Professor  Eichhoff,  of  Charlottenburg.* 
He  furnishes  a  number  of  figures  for  the  output  and  power  con- 
sumption of  Heroult  furnaces,  from  which  the  following  may  be 
quoted  :~~ 

TABLE  XI. 

Operation  o!  5=ton  Heroult  Furnace. 


Generator  K.W.  hrs. 

capacity.  Length  of  heat,     per  ton. 

once.. 6. 05  hrs.  725 

twice.  .6.63     "  795 


\  *  Drawing       ^ 

L     ^rr»-K"   \V          clno- 


With 

cold        -   750-K.W.  I  slag. 


thrice.  7. 22  868 


J/3r^  *"&•  j 

I  J 

With      )  /      With  only  one  slag.  .2.08     "  219 

hotil      -    643-K.W.  \  Drawing      }    f     once.. 2. 57  265 

charge)  (slag.  j[    twice.. 3. 15  324 

*European   Commission  Report,  pp.   53-55,   charges   658   and  660. 
•f-Better   results   have   been   obtained   more  recently,    see  Table    XI. 

The  long    ton   of  2,240  Ibs.    is    employed   in   this    chapter. 
•^European    Report,    pp.    85-89,    and   p.    115. 

gStahl  und  Eisen,  1907,  No.  2,  pp.   50-58,  and  Dr.  Haanel's   1907  Report,  pp. 
]!  Molten   steel   from    the   open-hearth   furnace. 


9O  THE     ELECTRIC     FURNACE. 

With  regard  to  the  possibility  of  making  structural  steel  in 
the  Heroult  furnace,  it  should  be  remembered  that  the  material 
of  the  charge  would  be  largely  pig  iron  and  ore,  as  there  would 
not  be  sufficient  scrap  available,  and  this  would  increase  the 
time  and  electrical  energy  required  for  the  operation.  On  the 
other  hand  the  pig  iron  could  be  charged  molten,  and  the  purifica- 
tion of  the  metal  need  not  be  carried  so  far  as  was  necessary  for 
tool  steel,  while  the  larger  scale  of  the  furnace  would  also  reduce 
the  consumption  of  electrical  energy  per  ton  of  product.  A  50- 
fcon  furnace  might  be  expected  to  require,  with  a  cold  charge, 
about  5,000  kilowatts,  or  about  50,000  amperes  at  no  volts  ;  while 
40,000  amperes  might  be  sufficient  if  molten  pig  iron  were  used. 

The  cost  of  making  structural  steel  in  a  5O-ton  Heroult 
furnace,  if  a  furnace  of  this  size  could  be  successfully  operated, 
would  probably,  with  electrical  energy  at  $10.00  a  horse-power 
yar,  be  about  the  same  as  in  a  gas-fired  open-hearth  furnace 
using  coal  at  $3.00  a  ton.  Assuming  that  the  general  cost  of 
operating  the  two  furnaces  was  the  same,  there  remains  fpr  the 
Heroult  electric  furnace  the  cost  of  electric  energy,  which,  at  o.  10 
horse-power  years  per  ton  would  be  $1.00  per  ton,  and  the  cost 
of  electrodes,  which  are  stated  to  cost  20  cents  per  ton ;  while  for 
the  open-hearth  furnace  there  is  the  cost  of  coal,  which  at  700  Ibs. 
per  ton  would  be  $1.00  and  the  cost  of  operating  the  gas  pro- 
ducers and  checker  chambers,  which  would  more  than  balance  the 
cost  of  electrodes.  Until  larger  furnaces  have  been  built,  it  is 
not  worth  while  to  attempt  to  estimate  in  detail  the  cost  of  operat- 
ing them,  but  the  figures  given  are  enough  to  show  that  under 
favorable  conditions,  large  electric  furnaces  might  be  expected  to 
compete  with  gas-fired  furnaces  for  the  manufacture  of  structural 
steel. 

A  Heroult  furnace  for  the  production  of  50  tons  of  steel  a  day 
has  been  installed  in  the  plant  of  the  Halcomb  Steel  Co.,  in 
Syracuse,  and  it  is  likely  that  this  will  lead  to  further  develop- 
ments in  size  and  efficiency.  The  furnace  is  being  used  in  con- 
junction with  gas-fired  furnaces,  and  is  charged  with  molten 
superoxidized  steel  from  a  Wellman  furnace,  the  operation  of  re- 
fining being  finished  in  the  electric  furnace. 

An  illustrated  description  of  such  a  plant  appeared  in  the 
Electrochemical  Industry,  vol.  v.,  p.  272,  from  which  the  follow- 
ing particulars  are  taken: — The  steel  is  made  from  scrap,  etc., 
in  a  Wellman  open-hearth  furnace  holding  25  tons.  The  opera- 
tion is  carried  further  than  in  ordinary  open-hearth  practice,  until 
the  carbon  and  phosphorus  have  been  almost  entirely  eliminated ; 


IRON*     AND     STEEL. 


the  removal  of  the  sulphur  and  oxygen  and  the  recarburization  of 
the  steel  being  effected  in  the  Heroult  furnace.  4  tons  of  highly 
oxidized  metal  from  the  open-hearth  furnace  are  transferred  to  the 
electric  furnace,  which  requires  i  V2  hours  to  finish  this  charge  of 
steel,  and  has  a  daily  output  of  60  tons.  At  the  high  temperature 
of  the  electric  furnace  very  basic  slags  can  be  used  which  will  re- 
move very  thoroughly  any  sulphur  remaining  in  the  steel,  and  in 
the  neutral  atmosphere  of  this  furnace  the  steel  can  be  deoxidized 
far  more  completely  than  is  possible  in  open-hearth  practice,  the 
slag  on  the  molten  steel  becoming  quite  neutral  or  free  from  iron 
oxide.  Such  steel  will  be  more  sound  than  the  usual  open-hearth 
product.  The  location  of  the  plant  is  not  specified,  and  no  figures 
are  given  for  the  amount  of  power  emploved. 

The  Heroult  Electric  Steel  Plant  at  Remscheid,  Germany, 
has  been  in  operation  for  a  year,*  and  was  turning  out,  a  few 
months  ago,  25  tons  of  steel  per  day.  A  new  plant  of  four  times 
this  capacity  will  shortly  be  in  operation. 

The  uses  of  the  Heroult  steel  furnace  may  be  stated  as  fol- 
lows : — 

(a)  The  production  of  tool  steel  and  other  high  grade  steels 
by    melting    pure    materials    just    as     in    the    crucible    process. 
Electric  furnace  steel  is  less  expensive  than  crucible  steel,  and  is 
also  sounder  and  more  tough. 

(b)  The  production  of  high  grade  steel  from  less  pure  ma- 
terials by  keeping  them  in  a  molten  condition  beneath  oxidizing 
slags,  which  are  repeatedly  changed  until  all  the  impurities  are 
removed.       In  this  process  the  pig  iron  which  forms  a  part  of  the 
charge  will  preferably  be  supplied  from  the  blast  furnace,  in  the 
molten  state. 

(c)  The  electric  furnace  may  be  used  for  finishing  steel  which 
has    been   practically   freed   from  carbon  and  phosphorus   in    the 
Bessemer  or  open-hearth  furnace. t 

The  following  special  features  of  this  electric  furnace  may  be 
noticed : — 

(a)  The  high  temperature  of  the  furnace  which  enables  very 
basic  slags  to  be  used. 

(b)  The  ability  to  exclude  the  air,  and  to  finish  the  charge 
under  slags  which  are  practically  free  from   oxide  of  iron,   thus 
obtaining  a  sounder  product. 


*Electrochemical    Industry,    vol.    v.,    pp.    25,    58,    and    198. 

fSee  P.  L.  T.  Heroult,  U.  S.  Patent  807,026,  Electrochem.  Industry,  vol.  iv.,  p.  31, 
for  converting  cast  iron  into  high-grade  steel  by  the  Bessemer  converter  followed  by 
the  electric  furnace. 


92  THE     ELECTRIC     FURNACE. 

(c)  The  slag  is  considerably  hotter  than  the  metal  and  will 
therefore  be  fluid  enough  to  act  freely  on  the  metal  without  the 
latter  being  overheated.     With  regard  to  the  possible  overheating 
of   the   steel   in   electric   furnaces   nothing   definite  appears  to   be 
known,  but  it  is  considered  that  if  steel  is  overheated  in  the  pres- 
ence of  basic  slags  it  will  absorb  nitrogen  and  become  less  tough 
in  consequence.*     In  the  electric  furnace,  however,  even  nitrogen 
is  largely  excluded  by  the  gases  arising  from  the  operation,  as  no 
air  or  other  gas   need   be   introduced   from  without. 

(d)  In  the  final  or  recarburizing  stage  in  the  electric  furnace, 
the  conditions  are  so  strongly  reducing  and  the  temperature  is  so 
high  that  even  calcium  carbide  is  formed  in  the  slag.      There  is 
therefore  practically   no   waste  of   the   ferro-manganese   or   other 
metallic  additions,  which  are  of  course  made  in  the  furnace  itself 
and  not  in  the  ladle. 

(e)  The  cost  of  the  electric  process  is  decidedly  less  than  that 
of  the  crucible  process,  and  special  varieties  of  steel  can  be  made 
commercially  in  the  electric  furnace,  in  places  where  cheap  power 
can  be  obtained.       The  largest  furnace  which  has  been  operated 
up  to  the  present  holds  about  5  tons,  and  the  number  of  kilowatt 
hours  per  ton  of  steel  produced  in  such  a  furnace  varies  from  800 
or  900,  when  cold  stock  is  employed  and  is  purified  by  repeated 
treatments  with  fresh   slags,   to  about   200  when  it  is  merely  re- 
quired to  finish  a  charge  of  steel  from  the  open-hearth  furnace. 

Mr.  Heroultt  has  proposed  an  electrically  heated  steel  mixer 
of  300  or  400  tons  capacity,  to  receive  the  steel  from  a  number  of 
open-hearth  or  Bessemer  furnaces,  thus  ensuring  a  uniform  pro- 
duct, and  allowing  a  more  perfect  deoxidation  of  the  steel  and 
separation  from  the  slag  than  by  the  usual  process  of  casting. 
Prof.  Richards  has  suggested  the  use  of  electrical  heating  as  an 
auxiliary  in  an  ordinary  open-hearth  furnace,  for  raising  the 
temperature  of  the  steel  through  the  last  100°  or  2oo°C.  before 
tapping,  as  a  little  electrical  heat  for  reaching  the  highest 
temperature  would  sometimes  save  a  good  deal  of  time  and  fuel. 

Keller  Steel  Furnace. J  This  is  substantially  the  same  as  the 
Hcroult  steel  furnace  and  need  not  be  further  described. 


*Journ.    Iron    and    Steel    Inst.,    1905,    No.    II.,   p.   777,    and   1906,   No     IV.,   p.    923. 
fP.    L.    T.    Heroult,    U.    S.    patent  807,027,    see    Klectrochem.    Industry,    vol.    iv.,    1906, 
P-    30. 

+  European    Report,    p.    77,    and   Electrochemical   Industry,   vol.    i.,    1903,    p.    162. 
Albert   Keller,    Journ.    Iron    and    Steel    Inst.,    19*3,    I.,   p.    178. 


IRON     AND     STEEL. 


93 


Sect 


Fig.  24.— The  Kjellin  Steel  Furnace. 

The  Kjellin  Furnace,  is  of  the  induction  type,  and  resembles 
a  step-down  transformer.  In  Fig.  24,*  which  represents  a  225 
horse-power  furnace  at  Gysinge,  Sweden,  A  is  the  primary  wind- 
ing to  which  an  alternating  current  of  90  amperes  at  3,000  volts 
is  supplied.  B  is  a  circular  trough  containing  the  molten  steel, 
and  corresponding  electrically  to  a  secondary  winding  of  one  turn. 
C  is  the  magnetic  circuit  \vhich  passes  through  both  the  primary 
and  the  secondary  windings.  The  alternating  current  in  the 
primary  windings  induces  an  alternating  current  in  the  ring  of 
molten  steel;  this  secondary  current  being  estimated  at  30,000 
amperes  and  7  volts.  This  furnace  has  the  great  advantage  of 
requiring  no  electrodes,  which  is  not  only  a  gain  as  regards 


'European  Report,  Figs,   i   and   2,  and  pp.  1-4. 


94  THE     ELECTRIC     FURNACE. 

trouble  and  expense,  but  avoids  any  contamination  of  the  steel  by 
the  material  of  the  electrode.  The  heat  is  generated  uniformly 
throughout  the  steel,  which  is  contained  in  a  closed  receptacle, 
under  conditions  which  resemble  those  of  the  crucible  steel 
furnace.  The  electrical  furnace  has,  however,  the  advantage  of 
holding  as  much  steel  as  many  crucibles,  and  of  being  quite  free 
from  the  furnace  gases  which  are  liable  to  enter  even  a  closed 
crucible. 

Compared  with  the  Heroult  furnace,  the  Kjellin  furnace  has 
the  objection  that  the  annular  groove  containing  the  steel  is  very 
long  in  comparison  with  its  cross  section,  which  will  cause  the  loss 
of  heat  to  be  excessive  and  the  weight  of  steel  to  be  small  for  a 
furnace  of  a  given  size.  The  furnace  does  not  form  a  very  efficient 
transformer,  and  it  appears  to  be  limited  in  size,  the  power  factor 
becoming  smaller  as  the  furnace  becomes  larger,  unless  the 
frequency  of  the  current  is  correspondingly  reduced.*  On  the 
other  hand  the  current  can  be  used  at  high  voltages,  such  as  3,000 
or  even  5,000  or  6,000  volts,  which  would  permit  of  the  genera- 
tion of  the  current  and  its  transmission  over  moderate  distances 
without  the  use  of  a  step-down  transformer  at  the  furnace. 

The  Kjellin  furnace  was  in  operation  at  Gysinge,  Sweden, 
when  visited  by  the  Commission  in  1904,  and  was  usually  making 
a  high  class  of  tool  steel  from  pure  pig  iron,  steel  scrap  and  bar 
iron,  for  which  purpose  it  seems  particularly  adapted.  In  operat- 
ing the  furnace  the  molten  steel  from  one  run  is  not  tapped  out 
completely,  but  about  one-third  of  it  is  left  in  the  groove  to  act  as 
a  conductor  to  carry  the  current  at  the  beginning  of  the  next  run  ; 
the  fresh  charge  of  charcoal  pig  iron  and  pure  iron  or  steel  scrap 
is  added  to  the  superheated  steel  as  fast  as  it  can  take  it  without 
chilling.  No  refining  is.  attempted  in  this  furnace,  the  operation 
being  merely  one  of  melting  a  metallic  charge,  made  up  in  correct 
proportions  to  give  a  steel  of  the  right  composition. 

The  furnace  is  built  in  a  circular  iron  casing,  LL,  which  is 
lined  with  fire  brick  at  EE.  The  trough  H  is  surrounded  with 
more  refractory  material,  DO,  for  which  either  magnesite  or  dolo- 
mite bricks  can  be  employed.  The  open  space  in  the  middle  of 
the  brick  work,  serves  to  cool  the  primary  winding,  by  the  current 
of  air  passing  through  it.  Water  jackets  are  also  employed  to 
protect  the  winding  from  the  heat  of  the  furnace.  The  groove 
B  is  covered  by  a  series  of  movable  lids  to  retain  the  heat  as  far 
as  possible,  and  any  of  these  can  be  removed  for  charging  the 

*In    more    recent    furnaces    this    difficulty    has    been    partly    overcome. 


IRON     AND     STEEL. 


95 


furnace.  At  the  end  of  the  operation  the  steel  is  tapped  from 
the  furnace  by  the  spout  H. 

In  one  run*  the  furnace  contained  about  1,500  Ibs.  of  steel 
from  the  previous  charge,  and  the  fresh  charge  of  best  Swedish 
pig  iron,  steel  scrap  and  Walloon  bar  iron  weighed  about  2,300 
Ibs.  Small  amounts  of  silicon-pig  and  ferro-manganese  were 
added  in  the  furnace,  and  2,271  Ibs.  of  good  quality  tool  steel  were 
obtained.  Samples  of  this  steel  were  tested  chemically  and  me- 
chanically by  Mr.  Harbord  with  satisfactory  results.  The  power 
employed  was  nearly  150  kilowatts  and  the  run  lasted  6  hours. 
The  energy  consumed  amounted  to  0.13  horse-power  years,  or 
850  K.W.  hours  per  ton  of  steel  ingots.  The  power  factor  at 
full  load  was  only  0.635  with  a  current  frequency  of  13^2  cycles 
per  second. t  It  will  be  seen  that  the  consumption  of  energy  for 
a  ton  of  tool  steel  is  less  than  in  the  Heroult  furnace ;  but  it  must 
be  remembered  that  in  the  latter,  miscellaneous  scrap  was  em- 
ployed and  washed  with  basic  slags  until  free  from  phosphorus 
and  sulphur,  after  which  it  had  to  be  recarburized  to  obtain  tool 
steel,  while  in  the  Kjellin  furnace  only  the  purest  materials  were 
employed,  and  they  merely  needed  to  be  melted  together  in  order 
to  produce  steel.  On  account  of  its  smaller  capacity,  the  Kjellin 
furnace  will,  no  doubt,  use  more  electrical  energy  than  the  Heroult 
for  the  same  amount  of  useful  work,  but  this  difference  in  efficiency 
does  not  appear  to  be  very  great  and  may  be  more  than  offset  by 
the  absence  of  electrodes  with  their  regulating  appliances,  heavy 
cables,  and  low  voltage  transformers.  In  other  words,  the 
Kjellin  furnace  may  be  expected  to  hold  its  own  for  certain  classes 
of  work,  in  competition  with  the  Heroult  furnace. 

The  Kjellin  furnace  has  been  used  for*  high  carbon  steel 
making,  but  attempts  were  made,  for  the  Commission,  to  make 
medium  and  low  carbon  steel  in  this  furnace  ;  and  while  the  at- 
tempts were  not  very  successful,  mainly  because  there  was  not 
sufficient  electrical  power  to  melt  the  more  refractory  mild  steel, 
it  appeared  probable  that  with  a  little  more  power  any  variety  of 
steel  could  be  produced  in  the  Kjellin  furnace. 

During  the  year  ending  May  3ist,  1906,  a  furnace  at  Gysinge, 
giving  i  ton  of  steel  per  tap,  has  produced  950  tons  of  steel 
and  special  steel  ingots. t 


*European  Report,  Charge  No.   546,  pp.   59-61,  and  47-48. 

fE.  C.  Ibbotson,  Journ.  Iron  and  Steel  Inst.,  1906,  No.  III.,  p.  397.  Electrochemical 
Industry,  vol.  iv.,  p.  350. 

tFurther  particulars  of  the  furnaces  at  Gysinge  are  contained  in  a  report  by 
V.  Engelhardt,  Stahl  u.  Eisen,  1905,  and  Electrochemical  Industry,  vol.  iii.,  (1905),  p. 
294. 


96  THE     ELECTRIC     FURNACE. 

More  recent  data  with  regard  to  the  furnace  at  Gysinge  are 
given  by  the  American  Electric  Furnace  Co.*  They  state  that 
the  furnace  requires  for  its  operation  165  to  170  kilowatts,  and 
has  a  capacity  of  3,000  Ibs.  of  metal,  of  which  about  1,850  Ibs. 
are  tapped  out  at  the  end  of  each  heat.  The  length  of  a  heat  is 
four  hours,  and  the  consumption  of  energy,  when  all  the  charge  is 
cidded  cold,  is  800  kilowatt  hours  per  ton.  Working  with  hot 
metal  from  the  blast  furnace  a  larger  output  and  greater  econonry 
is  obtained.  This  is  partly  because  the  furnace  can  be  com- 
pletely emptied  after  each  heat,  as  it  can  easily  be  restarted  by 
pouring  in  a  charge  of  molten  pig  iron.  Thus  a  charge  of  1,430 
Ibs.  of  molten  pig  iron  was  poured  into  the  empty  furnace,  and 
2,860  Ibs.  of  cold  pig  and  scrap  were  added.  In  six  and  three- 
quarter  hours  with  182  K.W.  the  charge  was  finished,  the  con- 
sumption of  energy  being  650  kilowatt  hours  per  ton  of  steel  in- 
gots. The  waste  of  material  during  the  melting  operation  is 
found  to  be  2%,  and  the  furnace  lining  will  last  for  twelve  weeks, 
costing  about  sixty  cents  per  ton  of  steel.  Purchasing  electrical 
energy  at  ^  cent  per  kilowatt  hour,  and  using  cold  material  in 
the  furnace,  the  electrical  energy  will  cost  a  little  more  than  the 
fuel  in  the  crucible  process,  but  a  great  economy  is  effected  by 
avoiding  the  use  of  crucibles.  The  cost  for  labor  is  also  much 
less  in  the  electrical  method. 

The  Colby  Steel  Furnace.  More  than  ten  years  before  the 
invention  of  the  Kjellin  furnace,  Mr.  Edward  Allen  Colby  had 
patented  an  induction  furnace  for  melting  metals. t  In  one  of  his 
first  patents, t  the  primary  winding  is  shown  surrounding  the 
circular  channel,  instead  of  being  within  it  as  in  the  Kjellin 
furnace;  the  furnace  tilts  in  order  to  pour  the  charge,  and  is 
covered  with  a  hood  for  the  purpose  of  excluding  the  air ;  the 
hood  being  arranged  so  that  the  molten  metal  could  be  poured  into 
a  mould  without  being  exposed  to  the  air. 

In  his  later  furnaces,  however,  the  primary  winding  has  been 
placed  within  the  secondary  as  in  the  Kjellin  furnace,  and  the 
covering  hood  has  been  discarded,  but  the  arrangement  for  tilt- 
ing the  furnace  in  order  to  pour  its  contents  is  still  employed. 

About  two  years  ago  Mr.  Colby  and  Dr.  Leonard  Waldo§ 
produced  the  first  steel  made  in  the  induction  furnace  in  the  United 

*Amcriran  Electric  Furnace  Co.,  45  Wall  Street,  New  York.  Bulletin  No.  i,  June, 
1907. 

•f-U.  S.  patents  428,378,  428,379,  and  428,552,  of  May  2oth,  1890.  See  Electrochemical 
Industry  vol.  Hi.,  p.  134. 

+  U.    S.   patent  428,552,   see  Electrochemical   Industry,    vol.   iii.,   (1905)  ;   Fig.    3,    p.    299. 

^Electrochemical    Industry,   vol.    iii.,    (1905),    p.    185. 


IRON     AND     STEEL. 


97 


States,  and  at  the  present  time  a  Colby  furnace  holding  190  Ibs. 
of  crucible  steel  is  in  operation  at  the  works  of  Henry  Disston  & 
Sons,  near  Philadelphia,*  and  several  much  larger  furnaces  are  in 
process  of  construction. 


I  I  I 


Fig.  25. — Colby  Induction  Furnace. 

The  small  furnace  in  use  at  the  Disston  steel  plant  is  shown 
in  the  frontispiece,  and  diagramatically  in  Fig.  25. t  It  consists 
of  a  laminated  iron  core,  around  which  is  a  primary  winding  of 
28  turns  of  thick  walled  copper  tube,  P,  and  an  annular  crucible, 
C,  containing  the  steel,  S,  which  forms  the  secondary  circuit  of 
the  transformer.  The  whole  furnace  tilts  to  pour  the  molten 
steel,  rotating  about  an  axis  indicated  by  the  line  XY.  The 
primary  winding  can  be  cooled  very  efficiently  by  water  circulat- 
ing through  the  copper  tube,  of  which  it  is  composed,  and  can 
therefore  be  placed  in  close  proximity  to  the  secondary  circuit 
without  any  danger  of  becoming  overheated.  The  arrangement 
of  the  coils,  as  shown  in  the  figure,  gives  far  less  opportunity  for 
magnetic  leakage  than  in  the  Kjellin  furnace  shown  in  Fig.  24, 
and  it  is  not  surprising  to  find  that  a  much  higher  power  factor 
has  been  obtained  ;  although  this  may  be  due  in  part  to  the  small 
size  of  the  Colby  furnace.  Mr.  Colby  gives  the  power  factor  as 
.93,  and  states  that  the  average  power  factor  after  the  charge  of 


*Trans.     Amer.    Electrochem.     Soc.,     vol.     xi.,     (1907). 
Electrochemical    Industry,   vol.    v.^    (1907),    p     232. 
fFrom    a   sketch   by   Mr.    Colby. 


98  THE    ELECTRIC    FURNACE. 

metal  is  fused  is  never  below  .90.  The  use  of  copper  tube  for 
the  primary  involves,  however,  the  employment  of  relatively  low 
voltage  current,  and  its  proximity  to  the  crucible  must  cause  con- 
siderable losses  of  heat,  although  this  will  be  guarded  against 
as  far  as  possible  by  a  packing  of  asbestos  or  other  heat  insulat- 
ing substance  between  the  crucible  and  the  copper  pipes.  The 
crucible  itself  is  made  of  graphite  and  clay,  being  similar  in  com- 
position to  the  graphite  crucibles  usually  employed  for  crucible 
steel  making.*  Such  crucibles  are  moderately  good  conductors  of 
electricity,  and  a  portion  of  the  secondary  current  will  no  doubt 
pass  through  the  crucible  itself,  thus  producing  heat  in  the  walls 
of  the  crucible  as  well  as  in  the  steel.  The  crucible  rests  upon  a 
slab  of  soapstone,  N,  and  is  jacketed  by  some  heat  insulating 
material,  J. 

The  following  data  in  regard  to  this  furnace  are  taken  in  part 
from  the  account  issued  to  the  American  Electrochemical  So- 
ciety, t  and  in  part  from  a  private  communication  from  Mr.  Colby 
to  the  author  :  — 

Crucible  capacity,  200  Ibs.  of  steel. 

Working-  capacity,   100  Ibs.   of  cast  steel  ing'ots  per  hour. 

Kilowatt  hours  per  100  Ibs.  of  cast  steel  ingots,,  35. 

Power  factor,  0.93. 

Maximum  kilowatts  with   190  Ibs.   steel  seldom  exceeds  43. 

Rated  size  of  furnace  for  crucible  steel  making-,  60  K.W. 

Primary  current  is  single  phase,  240  volt,  frequency  60,  less  than 

200  amperes. 

Secondary  current  about  9  volts  and  about  5,000  amperes. 
Length  of  operation,  i  hour  ;  half  of  which  is  required  for  fusion 

and   the  other  half  for  refining   and    "killing." 
Ingots  of  about  90  Ibs.  are  poured  every  hour,  the  remainder  of  the 

steel  being  left  in  the  crucible  for  starting  the  next  operation. 
Primary  winding,  28  turns  of  copper  tube  of  0-inch  internal,  and 
external  diameter. 


Induction  furnaces  under  the  patents  of  Colby  and  Kjellin  are 
now  constructed  in  the  United  States  by  the  American  Electric 
Furnace  Company  who  supply  furnaces  from  10  K.W.  upwards, 
and  of  the  stationary  or  tilting  variety.  They  publish!  the  follow- 
ing list  of  furnaces  in  operation  or  in  course  of  con- 
struction :  — 


*For  construction  of  the  Colby  crucible  see  U.  S.  patents  840,825  and  840,826,  de- 
scribed in  Electrochem.  Industry,  vol.  v.,  p.  55. 

•f-Trans.  Amer.  Electrochem.  Soc.,  vol.  xi.,  (1907),  and  Electrochemical  Industry, 
vol.  v.,  (1907),  p.  232. 

^American   Electric  Furnace  Co.,   Bulletin   No.   i,  June,  1907. 


IRON     AND     STEEL. 


99 


TABLE  XII. 

Induction  Furnaces  in  Operation  or  in  Course  of  Construction. 

Power 
No.     Amount     Capacity  required 


of  of 

furnace,   charge. 
Ibs. 


per  for 

24hrs.  operation 
Ibs. 
2,100 


k\v. 

40 

170 


18,480         80,000         736 


Disston    Steel    Works,    Phila- 
delphia, Pa i  150 

Gysinge,  Sweden    i  3,ooo         1 1,000 

International      Calcium      Co., 

Gurtnellen,  Switzerland      . .      i  7,500         22,400         320 

Roechling  Iron  Works,  Voelk- 

lingen,  Germany       i  130  480  75 

Roechling  Iron  Works,  Voelk- 

lingen,  Germany       i  660  2,500          no 

Roechling  Iron  Works,  Voelk- 
lingen,  Germany    •V;;ViVv*>     i 

Roechling  Iron  Works,  Voelk- 

lingen,  Germany       i        300,000          ... 

Krupp    Works,     Essen,     Ger- 
many       i          18,480         80,000         736 

Yickers'  Sons  &  Maxim,  Eng.      i  J,5oo  7,5°°         I3° 

Araya,  Spain       i  7,5°°         22,400         320 

Poldihutte  Co.,  Austria      i  7,500         22,400         320 

Guldsmedshyttan,  Sweden   -*>  — r .-.-.        7,500         22,400         320 

Note. — With  regard  to  the  apparent  discrepancy  between  some  of 
the  figures  in  this  table,  the  author  is  informed  by  the  American 
Electric  Furnace  Company  that  some  of  the  furnaces  do  not  conform 
tc  their  present  practice,  having  been  built  before  exact  knowledge 
was  available  for  the  most  efficient  design,  and  that  the  varying  con- 
ditions under  which  the  furnaces  are  working,  account  for  some  of  the 
seeming  discrepancies.  The  3oo,ooo-lb.  furnace  does  not  make  steel, 
but  is  an  electrically-heated  mixer  for  holding  molten  pig-iron  from 
the  blast  furnace.  All  the  furnaces  are  of  the  Kjellin  type  with  the 
exception  of  the  Colby  furnace  at  the  Disston  plant.  In  an  article  in 
the  Electrochemical  Industry,  (vol.  v.,  p.  172),  the  following  somewhat 
different  figures  are  given  for  some  of  the  above-mentioned  furnaces. 
Gysingen,  Sweden;  150  kw.,  955  kg.,  (2,100  Ibs.),  Voelklingen, 
Germany.  The  736  kw.  furnace  has  a  capacity  of  24  tons,  pouring 
15  tons  at  the  end  of  each  heat.  The  Vickers'  Sons  and  Maxim  works, 
Sheffield,  are  stated  to  have  a  200  kg.  (  ?  kw. )  furnace,  and  the  furnace 
at  Araya,  Spain,  is  stated  to  be  of  200  kw.,  no  capacity  being  given. 
In  resrard  to  the  Gysinge  furnace,  the  3,000  Ibs.  in  the  table  is  the 
capacity  of  the  furnace,  while  the  2,100  Ibs.  just  mentioned  is  the 
amount  poured  after  each  run.  When  molten  pig  iron  is  available, 
the  whole  charge  of  steel  can  be  poured  into  ingots  after  each  heat, 
but  in  other  cases  part  of  the  steel  must  be  left  in  the  furnace  to  start 
the  next  operation. 


100 


THE     ELECTRIC     FURNACE. 


The  induction  furnace  is  an  extremely  convenient  and  reason- 
ably economical  appliance  for  melting-  crucible  steel  and  other 
metals  and  alloys,  and  there  can  be  n.)  doubt  that  when  mere  melt- 
ing is  required,  as  in  the  production  of  crucible  steel  from  pure 
varieties  of  iron  and  ste':.:,  it  is  the  best  form  of  electric  furnace; 
and  that  when  electric  p  •  ,\ver  can  be  obtained  at  reasonable  rates, 
it  is  both  better  and  cheaper  in  operation  than  the  crucible  process. 

The  larger  sizes  of  induction  furnace,  such  as  would  be  used 
in  the  production  of  structural  steel,  appear  to  have  a  reasonably 
good  efficiency.  A  furnace  of  636  K.W.  is  stated  to  have  an  out- 
put of  30  tons  per  day  if  charged  with  cold  material,  and  36  tons 
when  charged  with  hot  metal.  These  figures  refer  to  the  pro- 
chi'^'cn  of  steel  from  ''pig  and  scrap,"  that  is  by  a  simple  melting 


Fig.  26. — 8-Ton  Induction  Steel  Furnace. 

operation,  and  correspond  to  expenditures  of  590  and  490  K.W. 
hours  respectively  per  ton  of  steel.  It  should  be  noted  that  these 
figures  are  apparently  the  results  of  calculations  by  Mr.  Engel- 
hardt,*  and  not  the  result  of  actual  operations.  About  the  same 

*Electrochemical    Industry,    vol.    iii.,    p.    ags. 


IRON     AND     STEEL.  IOI 

amount  of  electrical  energy  would  probably  be  needed  for  the 
simple  melting  of  pig  and  scrap  in  the  Heroult  furnace,  but  as 
this  furnace  is  generally  employed  for  purifying  as  well  as  merely 
melting  the  steel,  it  is  not  easy  to  make  an  exact  comparison. 

The  Gronwall  Furnace.  A  new  form  of  induction  steel 
furnace,  invented  by  Messrs.  A.  Gronwall,  A.  Lindblad  and  O. 
Stalhane,  is  illustrated  in  Fig.  26,  and  is  being  erected  in 
Sweden.*  This  furnace  embodies  certain  new  features  which 
enable  it  to  be  built  on  a  larger  scale  than  was  previously  possible, 
without  having  an  excessively  low  power  factor,  and  without  re- 
quiring current  at  unusually  low  frequencies. 

The  first  point  to  notice  is  the  trough  containing  the  steel. 
Instead  of  being  circular  as  in  the  Kjellin  and  Colby  furnaces,  this 
trough  has  a  semicircular  portion,  F,  passing  around  the  core,  E, 
and  a  folded  portion,  G,  extending  to  the  right  of  the  core.  This 
form  of  channel  has  the  advantage  of  being  more  compact  than  a 
circular  channel  of  the  same  length,  and  of  having  a  smaller  in- 
ductance. The  gridiron-like  construction  of  steel  channel  had 
been  employed  previously  by  G.  Gin,  Fig.  28,  but  its  application 
to  an  induction  furnace  is  new  and  appears  to  be  a  decided  im- 
provement. 

Another  new  feature  in  the  furnace  is  the  position  of  the 
primary  coil,  which  is  placed,  not  at  C,  as  in  the  earlier  forms, 
but  at  A,  around  the  outer  limb,  D,  of  the  transformer  core.  B 
and  C  are  compensator  coils  for  reducing  the  magnetic  leakage  of 
the  core. 

In  the  earlier  forms  of  induction  steel  furnace  a  serious 
difficulty  was  the  very  low  power  factor,  which  appeared  to  limit 
the  utility  of  this  type  of  furnace.  Lindblad  gives  the  following 
formula  for  the  power  factor  of  an  induction  furnace  : — 

c  n  a  f     i        i       J 
1  an   Y  —  "  -       I  r 

1  s   I  \YS     WP  J 
where, 

Y  =  angle  of  phase  displacement. 

n  =  frequency. 

a  =  area  of  cross  section  of  steel  in  the  channel. 

1  =  length  of  channel. 

s  =  specific  resistance  of  the  steel. 

c  =  a  constant. 

Ws  =  magnetic  resistance  around  secondary  circuit. 

WP  =  magnetic  resistance  around  primary  circuit. 

The  power  factor,  cos  Y,  is  highest  when  tan  Y  is  lowest  t 
that  is  when  the  magnetic  resistances  are  high,  the  frequency  low, 

*Dr.   Haanel's   1907  Report,   p.    101-104,   and  plates   x.-xii. 


IO2  THE     ELECTRIC     FURNACE. 

and  the  electrical  resistance  of  the  secondary  is  high.  The  very 
low  power  factors  of  the  earlier  furnaces  were  caused  by  the  ex- 
cessively low  electrical  resistance  of  the  secondary  circuit,  and 
the  necessarily  large  space  within  the  circular  steel  channel,  which 
afforded  an  easy  leakage  for  the  lines  of  magnetic  force.  It  be- 
came necessary  therefore  to  use  currents  of  very  low  frequency 
such  as  12  or  15  for  small  furnaces,  while  even  3  or  5  alternations 
were  proposed  for  larger  furnaces  ;  thus  requiring  special  electrical 
machinery,  and  making  it  impossible  to  draw  the  current  from 
ordinary  power  plants. 

In  the  new  furnace  the  steel  channel  turns  as  closely  as  pos- 
sible around  the  transformer  core,  and  yet  has  a  considerably 
greater  length,  thus  obtaining  an  increased  electrical  resistance 
of  the  secondary  circuit  and  a  greater  resistance  to  the  magnetic 
leakage  through  that  circuit.  The  primary  coil,  A,  is  placed  on 
the  outer  limb  of  the  core,  in  order  to  have  it  further  from  the 
hot  metal,  and  so  to  protect  the  insulation  of  the  coil  from  the 
heat  of  the  furnace.  This  arrangement  allows  of  the  use  of 
higher  voltage  current  in  the  primary  than  would  be  possible  in 
the  old  position. 

The  compensator  coils,  B,  and  C,  are  two  equal  coils  con- 
nected together  in  such  a  way,  that  if  the  magnetic  flux  in  D  and 
K  were  equal,  no  current  would  flow  in  B  or  C.  If,  however, 
leakage  occurs,  and  there  is  a  greater  flux  in  D  than  in  E,  a  cur- 
rent will  flow  in  the  coils  in  such  a  way  as  to  oppose  and  partly 
prevent  the  leakage.  An  external  source  of  electromotive  force 
may  also  be  used  to  maintain  a  current  in  the  coil,  C,  which  then 
becomes  an  auxiliary  of  the  main  primary  coil,  A. 

The  electrical  deficiencies  of  the  transformer  or  induction 
furnare  may  be  made  clearer  as  follows  : — In  an  ordinary  trans- 
former the  electric  current  flowing  in  the  primary  coil  sets  up  a 
magnetic  force  in  the  core,  and  this  force  passes  through  both  the 
primary  and  the  secondary  circuits.  The  alternating  current  in 
the  primary  is  constantly  changing  in  amount,  and  corresponding 
changes  take  place  in  the  magnetic  force  in  the  core.  The  changes 
in  the  magnetic  force  produce  an  electric  current  around  the 
secondary  circuit.  In  the  ordinary  transformer  the  primary  and 
secondary  windings  are  close  together  and  the  magnetic  force  set 
up  by  the  primary  must  pass  through  the  secondary  also,  but  in 
the  induction  furnace  the  secondary  winding  is  a  ring  of  molten 
steel  and  cannot  be  placed  close  to  the  primary  winding  without 
destroying  it.  The  magnetic  force  produced  by  the  primary  has 
therefore  a  chance  of  escaping  its  work  by  doubling  back  between 


IRON     AND     STEEL. 


103 


the  primary  and  the  secondary  coils.  The  arrangement  shown  in 
the  figure,  of  one  coil  on  each  limb  of  the  core,  makes  it  more 
difficult  for-  the  magnetic  force  to  escape  without  doing  its  work 
and  driving  an  electric  current  around  the  ring  of  molten  steel.  An- 
other deficiency  of  the  induction  furnace  arises  from  the  low 
electrical  resistance  of  the  secondary  circuit.  In  an  ordinary 
transformer  the  secondary  winding  is  connected  to  some  external 
resistance  or  other  load,  but  in  the  furnace  the  secondary  winding 
i?  shortcircuited,  and  having  a  very  low  resistance,  its  self — in- 
ductance will  be  high  as  compared  with  its  ohmic  resistance ;  and 
the.  current  produced  in  the  steel  will  consequently  be  far  less 
than  it  would  be  if  the  secondary  circuit  were  non-inductive,  or  the 
heat  produced  will  be  less  than  it  would  be  if  the  ohmic  resistance 
of  the  secondary  formed  a  larger  proportion  of  the  whole  re- 
sistance of  that  circuit.  The  gridiron  portion  of  the  steel  channel 
has  a  smaller  inductance  in  proportion  to  its  length  than  the 
circular  part  of  the  channel  and  consequently  increases  the  non- 
inductive  part  of  the  resistance  and  hence  the  effectiveness  of  the 
transformer. 


1 


M 


H 


Fig.  27. — Induction  Furnace  with  Shielded  Core. 

An  alternative  device  for  preventing  magnetic  leakage  con- 
sists of  a  copper  shield  or  mantle  around  the  core,  as  shown  at 
M  in  Fig.  27,  where  A  is  the  primary  coil  and  DEH  the  iron  core. 
The  lines  of  magnetic  force  cannot  pass  easily  through  this  shield, 
as  in  so  doing  they  would  produce  eddy  currents  in  the  metal  of 
the  shield,  and  these  eddy  currents  would  oppose  the  magnetic 
forces  which  started  them.  The  shield  must  not,  however,  form 
a  complete  ring  around  the  core,  as  it  would  then  act  as  a  chok- 
ing coil  on  the  primary  current.  It  must  therefore  be  made  in 
the  form  of  an  incomplete  cylinder,  as  at  (i)  or  a  spiral,  as  at  (2). 

The  furnace  in  Fig.  26  is  constructed  of  brickwork,  N,  in  a 
metal  container,  and  the  groove  containing  the  molten  steel  is 


104 


THE     ELECTRIC     FURNACE. 


IRON     AND     STEEL. 


'05 


constructed  in  some  more  refractory  material,  M,  such  as 
magnesite.  The  furnace  is  supported  on  two  piers,  P  P,  between 
which  space  is  left  for  the  transformer  core  D  E.  Three  spouts, 
S  S  S,  are  provided  at  different  levels;  the  upper  spout  serving  to 
remove  the  slag,  the  middle  spout  to  tap  off  the  usual  amount  of 
steel,  leaving  a  quantity  in  the  furnace  for  keeping  the  secondary 
circuit  unbroken,  and  the  lower  spout  for  emptying  the  furnace 
when  necessary. 

The  Gin  Steel  Furnace.*  Mr.  G.  Gin  invented  in  1897, t  a 
furnace  in  which  the  heat  is  generated  by  the  passage  of  a  large 
electric  current  through  a  groove  containing  molten  steel.  In 
the  Gin  furnace  the  induction  method  is  not  used,  but  the  current 
is  led  into  the  ends  of  the  canal  by  water-cooled  steel  electrodes, 
which  enter  from  below  and  form  part  of  the  furnace  lining.  In 
Fig.  28, t  A  is  the  groove  or  canal  containing  the  molten  steel,  a 
portion  of  which,  as  in  the  Kjellin  furnace,  may  be  left  in  the 
furnace  after  each  operation  to  start  the  current  for  the  next  run, 
and  B  B  are  the  water-cooled  steel  terminals.  On  account  of  the 
low  resistivity  of  molten  steel,  the  trough  or  canal  containing  it 
should  be  of  great  length  and  small  cross  section,  in  order  to 
avoid  the  use  of  excessively  large  currents.  This  was  advisable 
in  the  Kjellin  furnace,  but  it  is  even  more  necessary  in  the  Gin 
furnace,  because  the  current  must  be  developed  in  a  transformer 
and  led  to  the  furnace  by  cables,  all  of  which  are  more  expensive, 
for  equal  power,  as  the  current  is  larger  in  amount ;  and  the  trans- 
former and  cable  losses  are  also  very  large  when  enormous  cur- 
rents are  employed  at  low  voltages.  In  the  Gin  furnace  the 
trough  A  is  therefore  made  long  and  narrow,  and  in  order  to 
secure  compactness,  with  attendant  economy  of  heat,  it  is  folded 
backwards  and  forwards,  like  the  filament  in  an  incandescent 
lamp,  the  ends,  BB,  being  brought  to  the  same  end  of  the 
furnace. 

For  convenience  in  repairing  the  hearth,  it  is  mounted  on  a 
carriage  which  stands  in  a  furnace  consisting  of  three  walls  and 
an  arched  roof ;  the  fourth  side  being  closed  during  the  working 
of  the  furnace  by  a  movable  door.  H  is  one  of  the  two  spouts 
through  the  roof  for  introducing  molten  pig  iron.  The  pig  iron 
can  be  converted  into  steel  by  dilution  with  steel  scrap,  as  in  the 

*A  full  account  by  the  inventor  is  given  in  an  appendix  to  Dr.  Haanel's  Europear 
Report,  pp.  165-177.  Also  see  translation  by  P.  McN.  Bennie,  Electrochemical  Industry, 
vol.  ii.,  p.  20. 

•f-French  patent,  No.   263,783,  Feb.   6th,   1897 ;   see  European  Report,   p.   166. 
^Modified  from   figures   in    above  Report. 


IO6  THE     ELECTRIC     FURNACE. 

Kjellin  furnace,  or  by  additions  of  iron  ore,  as  in  the  Heroult 
furnace.  When  molten  pig-iron  is  employed  there  is  no  need 
to  leave  any  steel  in  the  furnace  from  the  previous  run.  The  steel 
is  tapped  from  the  furnace  by  means  of  the  spout,  K ;  three 
channels,  one  from  each  loop  of  the  canal,  leading  the  steel  to  the 
spout.  The  cables  for  leading  in  the  current  are  connected 
electrically  by  the  bars  GG,  to  the  lower  part  of  the  water-cooled 
terminals  BB.  A  700  kilowatt  furnace  would  have  a  canal  nearly 
30  feet  long,  9^  inches  wide  and  19%  inches  deep  ;*  and  it  would 
contain  8,550  Ibs.  of  steel,  which  would  about  half  fill  the  groove, 
and  would  require  a  current  of  about  50,000  amperes  at  15  volts. 

The  construction  and  maintenance  of  the  furnace  hearth  will 
probably  be  a  matter  of  considerable  difficulty ;  the  adjacent 
branches  of  the  canal  being  near  together  any  leak  of  metal  from 
one  to  the  next  would  lead  to  a  shortcircuiting  of  the  current  and 
a  rapid  enlargement  of  the  leak,  while  the  addition  of  iron  ore  in 
the  channels  will  lead  to  a  corrosion  of  the  walls.  The  best  ma- 
terial for  the  construction  of  the  hearth  would  probably  be 
chromite,  as  this  is  very  refractory  and  only  slightly  affected  by 
either  silicious  or  irony  slags. 

The  Gin  process  was  not  inspected  by  Dr.  Haanel,  as  the 
experimental  furnace  was  then  dismounted.  Mr.  Gin  gives  a 
full  account  of  his  process  in  Dr.  Haanel's  Report,  and  a  modified 
furnace  is  described  in  the  Electrochemical  and  Metallurgical  In- 
dustry, Vol.  III.,  p.  298,  but  no  experimental  results  are  given, 
so  it  will  be  well  to  suspend  judgment.  Mr.  Gin  has  also  de- 
scribed an  entirely  new  form  of  furnace  in  which  vertical  carbon 
electrodes  are  used.t  The  Gin  furnace  has  been  installed  at  the 
Plattenberg  Works,  Westphalia,!  the  Krupp  Works,  at  Essen, 
in  Germany,  and  the  Roechling  Iron  Works  at  Volklingen.§ 

The  Girod  Steel  Furnace,  recently  described  by  Dr.  R.  S. 
HuttonJ!  resembles  the  Heroult  steel  furnace  in  general  con- 
struction and  operation,  but  only  one  movable  electrode  is  em- 
ployed ;  the  return  connection  from  the  molten  steel  being  made 
by  means  of  water-cooled  steel  bars  embedded  in  the  hearth  of 
the  furnace.  For  a  small  furnace  the  single  electrode  may  be 
simpler  as  regards  construction  and  operation,  but  the  water- 
cooled  steel  bars  in  the  base  of  the  furnace  introduce  an  additional 


*European   Report,  p.    173. 

•f-Trans.    Amer.    Electrochem.    Soc.,    vol.    viii.,    p.    105. 
t  Electrochemical   Industry,  vol.    ii.,    p.    120,    and    vol.    Hi.,   p.    434. 
§Dr.   Haanel,   1907  Report,   p.    149. 

|jThe    Girod    Ferro-Alloy    Works    and   the    New    Girod    Steel   Furnace,    Electrochem. 
Industry,   vol.   v.,   p.    9.      See   also   vol.   iii.,    p.    434. 


IRON    AND     STEEL.  107 

* 

complication,  and  as  only  one  arc  is  employed,  instead  of  two 
arcs  in  series,  the  Aroltage  of  the  furnace  would  probably  be  lower, 
and  a  larger  current  would  be  required  to  supply  the  same  amount 
of  heat.  The  author  employed  a  small  furnace  of  this  type  (de- 
scribed at  the  end  of  this  chapter)  for  the  production  of  steel 
directly  from  the  ore,  in  order  to  avoid  the  use  of  the  carbon  lining 
which  is  usual  in  electric  ore  smelting  furnaces.  The  Girod 
crucible  furnace,*  is  not  employed  at  the  present  time  for  the 
manufacture  of  steel. 

Dr.  Haanel  gives  a  list  in  his  1907  report  of  twenty-two 
electrical  furnaces  in  operation  or  in  course  of  construction.  Of 
these  seven  are  Heroult  furnaces,  five  are  Kjellin  or  other  induc- 
tion furnaces,  two  are  Gin  furnaces,  two  Stassano,  one  Keller,  and 
one  Girod  furnace ;  beside  four  furnaces  of  unspecified  design 
(possibly  Heroult)  at  Allevard.  That  this  list  by  no  means  repre- 
sents all  the  steel  furnaces  that  are  now  in  operation  or  construc- 
tion will  be  evident  if  reference  is  made  to  Table  XII.,  in  which 
no  fewer  than  twelve  steel  furnaces  of  the  induction  type  alone  are 
listed.  It  is  intended  to  employ  Heroult  steel  furnaces  at  the  new 
electric  smelting  works  at  Welland  and  Baird,  to  treat  the  pig 
iron  produced  by  the  ore-smelting  furnaces. 

II. — Production  of  Pig  Iron  from  Iron  Ore,  Carbon  and  Fluxes. 

The  production  of  pig  iron  from  iron  ore  in  the  electric 
furnace  is  a  proposition  of  greater  commercial  importance  than 
the  'manufacture  of  tool  steel,  or  even  structural  steel ;  but  the 
process  is  in  a  less  advanced  condition.  The  electrical  smelting 
of  iron  ores  is  simple  in  principle ;  the  ore  being  mixed  with  suit- 
able fluxes,  as  in  the  blast  furnace,  and  with  sufficient  carbon  to 
reduce  the  iron  and  other  materials,  and  to  supply  carbon  to  the 
pig  iron.  The  electric  current  is  made  to  pass  through  the 
mixed  charge,  which  becomes  heated ;  the  iron  being  reduced  and 
carburized,  and  the  earthy  portions  of  the  ore  melted  into  a  slag. 
Less  carbon  is  needed  than  in  the  blast  furnace,  where  the  com- 
bustion of  carbon  supplies  the  heat.  This  saving  in  carbon  will 
offset  a  part,  and  in  some  cases  the  whole,  of  the  cost  of  the 
electrical  energy. 

Several  furnaces  have  been  constructed  for  the  electric 
smelting  of  iron  ores,  the  most  important  of  these  being  the 
Heroult  and  the  Keller  ore  smelting  furnaces,  and  modifications 
of  these. 


*See    Electrochemical    Industry,    vol.    ii.,    p.    309,    and    vol.    iii.,    p.    434. 


io8 


THE     ELECTRIC     FURNACE. 


,..JO 


12. 


J3ffc 


Fig.  29. — Heroult  Ore-smelting  Furnace. 

The  Heroult  Furnace.  The  experimental  Heroult  furnace,* 
(Fig.  29),  as  used  at  Sault  Ste.  Marie  in  the  spring  of  1906,  con- 
sisted of  a  nearly  cylindrical  shaft  in  which  a  carbon  electrode,  C, 
was  suspended.  The  furnace  was  built  inside  an  iron  casing,  N, 
4  feet  in  diameter,  bolted  to  a  cast  iron  bottom  plate,  H.  The 
lower  part  of  the  furnace  was  lined  with  carbon,  put  in  as  a  paste, 
and  this  carbon  lining  formed  the  lower  electrode  of  the  furnace, 
the  current  passing  between  C  and  G  through  the  melting  charge. 
One  cable  from  the  transformer  was  connected  to  H,  and  a  num- 
ber of  iron  rods,  I,  served  to  make  better  contact  between  the 


*Dr.  Ilaanel,  Report  on  Experiments  at  Sault  Ste.  Marie,  1907,  pp.  3  and  46,  and 
plate  vii.,  Paul  L.  T.  Jleroult,  U.  S.  patent  858,718;  see  Electrochem.  Industry,  vol.  v  / 
P  325- 


IRON     AND     STEEL.  IOQ 

bottom  plate  and  the  carbon  lining.  The  upper  part  of  the 
furnace  was  lined  with  common  fire  bricks,  but  the  carbon  lining 
was  continued  to  a  point  a  little  above  the  slag  level,  as  it  resists 
the  solvent  section  of  the  slag  much  better  than  firebrick.  The  in- 
terior of  the  furnace  tapered  a  little,  upwards  and  downwards 
from  the  point  at  which  the  brick  and  carbon  linings  met.  Two 
tapping  holes  were  provided,  the  lower  one  which  leads  to  the 
spout,  S,  for  the  pig  iron,  and  the  upper  one,  D,  for  the  slag. 
The  upper  electrode  was  supported  by  the  holder,  AB,  which  has 
already  been  described  (Chap.  IV.),  and  which  was  suspended  by 
a  chain  so  that  it  could  be  raised  or  lowered ;  the  regulation  of  the 
electrode  would  normally  be  automatic.  The  electric  current 
was  led  to  the  carbon  through  the  holder  AB. 

An  iron  casing  is  very  convenient  in  the  construction  of  any 
kind  of  furnace,  but  for  an  electric  furnace  using  an  alternating 
current,  the  complete  iron  ring,  N,  through  which  the  current  has 
to  pass,  would  be  very  objectionable,  as  it  would  increase  the 
inductance  of  the  circuit ;  thus  opposing  the  passage  of  the  cur- 
rent, and  lowering  the  power  factor.  On  this  account,  a  vertical 
strip  of  the  iron  case,  10  inches  wide,  was  replaced  by  a  copper 
plate. 

In  operating  the  furnace,  the  current  is  started  between  the 
electrode,  C,  and  the  bottom  of  the  furnace  (a  little  coke  could 
be  placed  in  the  furnace,  if  necessary,  to  prevent  too  large  a  rush 
of  current  on  making  contact),  and  the  ore,  mixed  with  charcoal 
and  fluxes,  is  fed  in  around  the  electrode.  The  heat  generated 
by  the  electric  current  will  heat  the  charge  around  the  end  of 
the  electrode,  and  as  the  charge  becomes  partly  reduced  and 
melted  it  will  carry  the  current  more  readily,  and  the  electrode 
can  be  gradually  raised  until  it  reaches  its  normal  position.  The 
part  of  the  furnace  between  C  and  G  may  be  considered  the  zone 
of  fusion,  and  contains  molten  pig  iron,  F,  molten  slag,  E,  and 
a  mixture,  D,  of  charcoal  and  melting  slag  and  metal. 

The  ore  charged  into  the  furnace  contains  iron  in  an  oxidized 
condition,  and  this  oxide  of  iron  is  reduced  by  the  charcoal,  form- 
ing metallic  iron  and  carbon  monoxide.  This  direct  reduction 
by  charcoal  probably  takes  place  mainly  in  the  lower  and  hotter 
part  of  the  furnace,  but  the  carbon  monoxide,  so  formed,  is  itself 
a  good  reducing  reagent  and  reacts  with  the  oxides  in  the  upper 
part  of  the  furnace,  partly  reducing  these  and  liberating  carbon 
dioxide,  which  is  again  reduced,  in  part,  to  carbon  monoxide  by 
the  charcoal  in  the  charge.  The  reactions  may  be  represented 
as  follows : — 


IIO  THE     ELECTRIC     FURNACE. 


Fe2O3  +  CO  =  2FeO  +  CO2. 
FeO  +  C  =  Fe  +  CO. 


It  will  be  seen  that  the  gas  escaping  from  the  furnace  must 
be  rich  in  carbon  monoxide,  and  is  therefore  more  valuable  than 
the  gas  from  an  ordinary  blast  furnace  which  is  largely  diluted 
with  nitrogen  from  the  blast.  In  the  illustration  this  gas  is 
represented  as  burning  around  the  electrode,  above  the  charge, 
but  in  regular  practice  it  would  be  employed  to  preheat  the  charge. 
The  carbon  monoxide  will  not  reduce  the  iron  ore  until  the  latter 
has  become  somewhat  heated,  and  in  electric  smelting  the  heat 
will  not  penetrate  so  far  up  the  descending  column  of  ore  as  it 
does  in  the  blast  furnace,  as  there  is  a  much  smaller  flow  of  gas 
to  carry  the  heat.  The  shafts  of  electric  smelting  furnaces  will 
therefore  not  need  to  be  so  high,  in  proportion,  as  the  shafts  'of 
blast  furnaces.  In  figures  29  and  30  the  arrangement  of  the 
electrodes  would  also  prevent  a  high  furnace  from  being  used, 
but  this  has  been  modified  in  later  forms  of  the  furnace,  and  the 
volume  of  the  upper  part  of  the  furnace  may  be  effectively  in- 
creased if  the  ore  charge  is  preheated  by  the  combustion  of  the 
carbon  monoxide. 

Turning  now  to  the  results  obtained  in  this  furnace,  Dr. 
Haanel  reports*  that,  in  the  experimental  runs,  which  were  begun 
about  the  middle  of  January,  1906,  and  continued  until  the  5th  of 
March,  some  55  tons  of  pig  iron  were  electrically  smelted  from 
hematite,  magnetite,,  roasted  pyrrhotite,  and  titaniferous  ores, 
The  furnace  worked  satisfactorily  with  all  these  ores,  and  pig 
fron,  low  in  sulphur,  was  obtained  from  the  roasted  pyrrhotite, 
and  other  ores  of  high  sulphur  content.  Charcoal  forms  a  per- 
fectly satisfactory  reducing  agent,  and  this  is  important,  since  in 
Ontario  and  Quebec  charcoal  can  often  be  produced  cheaply  from 
mill  refuse,  wood  or  even  peat,  while  coke,  suitable  for  blast 
furnaces,  must  be  imported.  In  this  connection,  it  should  be  re- 
membered that  the  coke  or  charcoal  used  in  a  blast  furnace  should 
be  of  good  quality,  and  able  to  stand  the  weight  of  the  heavy 
column  of  ore  without  crushing  ;  while  in  the  electric  furnace  the 
quality  of  the  reducing  reagent  is  less  important,  and  broken 
charcoal  and  partly  charred  wood  was  found  to  serve  the  purpose. 
The  electric  furnace  differs  from  the  blast  furnace  in  the  absence 
of  a  blast  of  air,  and  in  the  possibility  of  attaining  a  higher 
temperature.  Both  of  these  differences  are  in  favor  of  the 

*Preliminary  Report,    1906,    p.    8. 


IRON     AND     STEEL.  Ill 

electric  furnace,  and  cause  it  to  be  a  more  powerful  reducing 
and  melting  appliance  than  the  blast  furnace.  The  strong  reduc- 
tion helps  to  drive  the  sulphur  into  the  slag,  as  calcium  sulphide, 
and  the  high  temperature  that  is  attainable  allows  a  very  limey  slag 
to  be  used  for  the  removal  of  the  sulphur.  Strong  reducing  condi- 
tions, although  desirable  as  removing  the  sulphur,  have  the  effect 
of  increasing  the  amount  of  silicon  in  the  pig  iron,  and  iron  con- 
taining as  much  as  5%  or  6%  of  silicon  was  obtained,  with  only 
0.06%  of  sulphur  when  smelting  the  roasted  pyrrhotite.*  Dr. 
Haanel  reports,  however,  that  by  increasing  the  limestone  in  the 
charge,  the  silicon  in  ferronickel  pig  has  recently  been  lowered  to 
2%.  With  less  sulphurous  ores  the  iron  could  be  obtained  high 
or  low  in  silicon  as  desired,  as  the  degree  of  reduction  in  the 
furnace  is  quite  under  control. 

The  consumption  of  electrical  energy,  in  horse-power  years 
per  ton  of  pig  iron,  varied  from  0.268  to  0.333  m  tne  later  runs 
on  iron  ores.t  If  the  carbon  monoxide  escaping  from  the  furnace 
were  utilized  for  preheating  the  ore  and  flux,  these  figures  would 
be  materially  reduced  and  somewhat  better  results  may  be  ex- 
pected from  furnaces  of  larger  dimensions,  and  when  the  condi- 
tions for  smelting  have  been  more  completely  ascertained.  The 
amount  of  charcoal  used  varied  from  30%  to  34%  of  the  weight 
of  the  ore,  or  about  1,100  to  1,260  Ibs.  of  very  poor  charcoal  per 
ton  of  pig. 

After  the  conclusion  of  Dr.  Haanel's  experiments  at  Sault 
Ste.  Marie,  the  plant  was  purchased  by  the  Lake  Superior  Power 
Company,  and  has  been  used  for  the  production  of  ferro-nickel 
pig  from  roasted  pyrrhotite.  t 

The  Keller  Furnace,  (Fig.  30), §  differs  from  the  Heroult  in 
having  two  vertical  shafts,  NN',  communicating  below  by  a  pas- 
sage, CC'.  Each  shaft  contains  a  carbon  electrode,  D,  and  the 
current  from  these  electrodes  flows,  normally,  through  the  molten 
metal  K  in  CC',  but  permanent  carbon  electrodes,  BB',  connected 
electrically  by  a  copper  bar,  EE',  serve  to  carry  the  current  from 
one  shaft  to  the  other  whenever  the  furnace  is  empty.  H,  is  an 
auxiliary  electrode  which  may  be  employed  for  heating  the  metal 
in  K  if  it  should  ever  become  chilled. 

This  furnace  has  the  advantage  of  providing  a  receptacle, 
K,  for  the  molten  metal  and  slag ;  the  metal  being  tapped  through 
the  hole,  K,  and  the  slag  through  the  hole,  J.  The  receptacle, 

*i9t>7  Report,  p.  84. 

•f-1907  Report,  runs   ia  to   17  in  which  charcoal  was  used. 

£1907  Report,  pp.   93-95 

§Dr.    Haanel's    European    Report,    1904. 


112 


THE     ELECTRIC     FURNACE. 


Fig.  30.— The  Keller  Furnace. 

K,  corresponding'  to  the  fore-hearth  or  settler  of  a  copper  furnace, 
receives  the  molten  products  of  two,  or  even  four  shafts,  thus 
reducing  the  labor  of  tapping  ;  and  the  use  of  two  shafts,  con- 
nected electrically  in  series,  enables  the  current  to  be  employed  at 
i*  higher  voltage  than  in  the  case  of  a  single  shaft  furnace.  The 
working  lining  of  the  furnace  is  made  by  ramming  a  mixture  of 
burnt  dolomite  and  tar  around  a  mould,  and  has  been  found  to 
stand  very  well.  As  the  heat  is  produced  in  the  centre  of  the 
shaft,  it  should  be  possible,  by  suitably  proportioning  the 
furnace  to  keep  the  walls  at  so  moderate  a  temperature  that  they 
might  be  built  of  ordinary  fire  brick,  as  in  the  blast  furnace.  Fire 
bricks  are,  however,  rapidly  corroded,  even  at  moderate 
temperatures,  by  slags  containing  oxide  of  iron,  and  would  only 
stand  if  the  conditions  were  so  strongly  reducing  as  to  convert 
the  whole  of  this  oxide  to  metal.  It  will  be  remembered  that  the. 
working  lining  of  the  Heroult  furnace  was  carbon,  which  is  in- 


IRON     AND     STEEL.  1 13 

fusible  and  does  not  corrode  unless  exposed  to  oxygen  or  metallic 
oxides,  such  as  iron  oxide.  Such  a  lining  will  last  if  the  furnace 
conditions  are  strongly  reducing,  and  cast  iron  is  being  made, 
but  would  not  last  if  it  were  attempted  to  produce  steel  in  the 
furnace,  as  there  would  be  a  considerable  amount  of  iron  oxide 
in  the  slag.  A  basic  lining,  such  as  dolomite,  would  then  have 
to  be  used. 

The  ore  enters  the  furnace  through  iron  hoppers,  MM',  which 
are  provided  with  an  annular  space,  L,  into  which  the  gases  from 
N  can  easily  escape  instead  of  passing  up  through  the  ore  in  M. 
From  L  the  gases  are  withdrawn  in  pipes  and  utilized  in  any 
suitable  manner,  such  as  running  a  gas  engine  or  preheating  the 
ore.  The  iron  casing,  round  the  furnace  inspected  by  Dr.  Haanel, 
was  the  cause  of  a  very  low  power  factor  being  obtained,  and  it 
will  be  omitted  or  modified  in  the  future. 

The  Haanel  Commission  visited  the  works  of  Messrs.  Keller, 
Leleux  &  Co.,  at  Livet,  France,  in  March,  1904,  and  during  their 
visit  some  30  tons  of  ore  were  smelted  electrically.*  The  ore 
was  hematite  and  contained  48.7%  of  iron  and  10%  of  moisture. 
Coke,  containing  7.6%  of  ash  and  91.1%  of  fixed  carbon,  was 
used  for  reducing  the  ore,  and  the  amount  required  varied  from 
about  1 8%  to  20%  of  the  ore,  from  17%  to  19%  of  ,the  ore  and 
fluxes,  or  from  800  to  900  Ibs.  per  ton  of.  pig  iron.  The  energy 
used,  per  ton  of  pig,  was  .532  E.H.P.  years  in  the  first  experi- 
ment, and  .253  E.H.P.  years  in  the  second  experiment.  In  the 
first  experiment  the  furnace  was  working  badly,  and  the  experi- 
ments at  Sault  Ste.  Marie  tend  to  show  that  the  smaller  of  these 
figures  may  be  considered  reliable. 

The  Harmet  Furnace  (Fig.  3i),t  differs  from  the  Heroult  and 
Keller  furnaces  in  having  the  electrodes  inserted  laterally  into  the 
lower  part  of  the  shaft  instead  of  passing  vertically  down  the 
furnace.  The  shaft,  S,  is  enlarged  below  to  allow  of  the  inser- 
tion of  the  electrodes,  EE,  and  the  current  passes  between  these 
through  the  melting  charge,  the  slag,  C,  and  the  molten  metal, 
B.  The  inclined  lateral  electrodes  will  probably  be  less  satis- 
factory in  actual  use  than  a  central  electrode,  because  it  will  not 
be  easy  to  regulate  the  current  by  raising  or  lowering  them  as  is 
done  in  the  other  furnaces ;  supporting  the  electrodes  in  this  posi- 
tion will  also  be  less  easy,  and  the  walls  will  be  apt  to  melt  around 
the  electrodes.  On  the  other  hand  the  height  of  the  shaft,  S,  is 


*European    Report,    pp.    90-109. 

•{•Treatise  on  Electro  Metallurgy  of  Iron,  by  Henri  Harmet,  European  Report.  1904, 
pp.    124-164.     Electrochemical   Industry,  vol.   i.,  (1903),   p.   422. 


THE     ELECTRIC     FURNACE. 


Fig.  31. — The  Harmet  Furnace. 

not  limited  as  in  the  Heroult  furnace,  by  the  length  of  the 
electrode ;  and  better  provision  can  be  made  for  the  pre- 
heating and  reduction  of  the  ore.  Harmet  utilizes  the  com- 
bustible gases  escaping  from  the  top  of  the  shaft,  for  burning,  in 
a  separate  furnace  or  calciner,  in  which  the  ore  is  calcined  and 
preheated  before  charging  into  the  main  furnace.  Some  of  the 
gas  is  returned  to  the  foot  of  the  shaft,  being  blown  in  at  this 
point  to  supply  a  reducing  gas  for  converting  the  iron  oxide  to 
metal,  and  to  carry  some  of  the  heat  from  the  crucible  up  the 
shaft,  so  as  to  preheat  and  reduce  the  descending  ore.  The 
use  of  the  gas  to  preheat  the  ore  before  charging  into  the  furnace 
is  very  desirable,  but  there  will  be  no  need  to  blow  gases  through 
the  smelting  shaft,  becau.^  reducing  gases  are  always  formed 
here  in  large^  amount,  ana  because  the  combustion  of  the  gas  jn 
the  calciner  would  heat  the  ore  to  a  temperature  at  which  it 


IRON     AND     STEEL.  115 

would  begin  to  be  reduced  to  the  metallic  state  directly  it  was  in- 
troduced into  the  smelting  shaft. 

Mr.  Henri  Harmet  has  written  a  treatise  on  the  electro- 
metallurgy of  iron,  which  is  printed  in  Dr.  Haanel's  European 
Report,  and  in  this  he  considers  every  conceivable  way  in  which 
iron  ores  can  be  reduced  by  the  joint  use  of  carbon  and  electrical 
heat,  but  no  mention  is  made  of  any  actual  furnace  embodying 
his  views — even  on  the  experimental  scale. 

Since  the  preceding  pages  were  written,  furnaces  have  been 
devised  on  a  larger  scale  and  with  important  improvements  in 
construction  and  design. 

The  Haanel=Heroult  Furnace,  shown  in  Fig.  32,*  is  an  im- 
provement on  Heroult's  earlier  furnace.  The  upper  electrode  no 
longer  descends  through  the  same  shaft  as  the  ore,  but  a  separ- 
ate opening  is  provided  for  it  into  the  smelting  zone  of  the 
furnace ;  while  two  lateral  shafts  are  provided  for  the  heating 
and  reduction  of  the  ore.  The  ore  shafts,  A  and  B,  can  thus  be 
made  of  any  desirable  height,  not  being  limited  by  the  length  of 
the  electrode ;  and  hoppers,  K  K,  can  be  used  for  charging  the  ore, 
thus  allowing  the  combustible  gases  to  be  led  away  through 
pipes,  L  L,  for  preheating  the  ore  or  other  purposes.  The  elec- 
trode, C  D,  also,  is  protected  from  heat  and  wear  except  at  the 
working  end,  C. 

The  stuffing-box,  F,  through  which  the  electrode  enters  the 
furnace,  is  needed  to  prevent  the  escape  of  gases.  It  is  made 
of  copper,  is  water-cooled,  and  is  packed  with  \vedge- 
shaped  rings  of  graphite.  The  graphite  packing  not  only 
makes  a  gas-tight  joint,  but  also  ensures,  an  electrical  contact 
between  the  electrode  and  the  stuffing-box,  so  that  the  electric 
current  can  be  led  to  the  electrode  by  the  arm,  G.  It  should  be 
noted  that  this  use  of  the  stuffing-box  for  electrode  holder,  not 
only  makes  it  serve  a  double  purpose,  but,  by  leading  the  current 
into  the  electrode  as  near  as  possible  to  its  working  end,  does 
away  with  all  needless  production  of  heat  by  the  passage  of  the 
current  through  the  electrode.  The  furnace  is  cased  with  steel 
plates,  but  the  top,  O,  and  a  strip  at  one  side,  P,  as  well  as  the 
stuffing-box,  are  made  of  copper,  so  as  to  avoid  a  complete  ring 
of  iron  around  the  path  of  the  current. 

The  furnace  is  shown  filled  with  ore,  flux  and  charcoal,  as 
it  would  be  during  operation,  and  with  molten  slag  and  metal  at 
S,  and  M.  These  are  drawn  off  through  three  tapping  holes 
and  spouts,  of  which  the  middle  and  lowest  spout  is  for  metal, 

*Dr.    Haanel's    Sault    Ste.    Marie  Report,    1907,    plate    ix.,    and   pp.    92-93. 


n6 


THE     ELECTRIC     FURNACE. 


Fig.  32. — Haanel=Heroult  Furnace. 


IRON     AND     STEEL.  1 1/ 

while  the  other  two  are  for  slag.  The  shafts  and  other  parts 
of  the  furnace  are  lined  with  fire-bricks,  but  the  part,  X,  which 
is  exposed  to  the  action  of  melting  ore,  slag  and  metal,  is  com- 
posed of  specially  refractory  material,  such  as  magnesite.  The 
arch  across  the  middle  of  the  furnace  will  also  be  particularly 
liable  to  corrosion  and  wear,  but  will  be  somewhat  protected  by 
the  cooling  effect  of  the  stuffing-box. 

The  lower  electrode,  E,  consists,  as  in  the  earlier  furnace,  of 
a  rammed  carbon  plug,  making  contact  with  the  aid  of  iron  spikes 
to  the  heavy  cast  iron  bottom  plate  and  so  to  the  contact  piece,  J. 
The  upper  electrode  is  made  cylindrical,  to  allow  of  its  passage 
through  the  stuffing-box.  Additional  lengths,  D,  are  attached 
by  threaded  joints  as  shown  in  section  in  the  figure,  thus  avoid- 
ing any  interruption  in  operation  or  waste  of  electrode.  The 
piece  R,  clamped  on  the  electrode,  serves  to  hold  it  while  a  new 
piece  is  being  screwed  on,  and  also  for  raising  or  lowering  the 
electrode. 

No  scale  is  given  in  the  original  drawing,  which  is  merely 
intended  to  show  the  principles  on  which  the  furnace  would  be 
constructed. 

The  Turnbull=Heroult  Furnace,  Fig.  33,*  is  a  modification  of 
Heroult's  original  furnace  which  has  been  devised  by  his  Can- 
adian representative,  Mr.  R.  Turnbull.  As  shown  in  the  figure 
there  are  six  movable  electrodes,  descending  into  a  smelting 
groove  or  canal,  which  forms  a  closed  rectangle.  The  ore  de- 
scends in  a  central  shaft,  and  is  distributed  to  the  smelting  groove 
by  six  inclined  shoots,  one  descending  between  each  adjacent  pair 
of  electrodes.  The  number  of  electrodes  is  preferably  some 
multiple  of  three,  so  as  to  permit  the  use  of  three-phase 
current. 

The  three  electrical  connections,  a,  b,  and  c,  on  the  bottom 
of  the  furnace,  appear  to  indicate  that  the  secondary  windings 
of  the  three  transformers  are  not  connected  together,  but  that 
the  cables  from  one  end  of  each  are  connected  to  A  A,  B  B,  and 
C  C,  respectively,  while  the  return  cables  are  all  connected  to  the 
common  terminal  a  b  c,  on  the  bottom  plate  of  the  furnace.  The 
wiring  for  this  arrangement  is  shown  in  Fig.  34,  in  which  Xd, 
Yd,  and  Zd  are  the  secondary  windings  of  the  transformers, 
each  of  which  is  connected  to  the  furnace  by  two  cables,  one  lead- 
ing to  a  pair  of  movable  electrodes  and  the  other  to  the  bottom 
of  the  furnace.  It  will  be  evident  that  by  connecting  the  secondary 
windings  in  Y  form  as  in  Fig.  35,  the  return  cables  from  a  b  c  to 

*Dr.    Haanel's   Sault   Ste.    Marie   Report,   1907,  plate   xviii.,    and   p.   147. 

9 


u8 


THE     ELECTRIC     FURNACE. 


=LJ 


Fig.  33. — The  Turnbull=Heroult  Furnace, 


IRON     AND     STEEL. 


D  will  be  unnecessary,  as  each  cable  and  pair  of  electrodes  will 
serve  as  a  return  for  the  other  cables  and  electrodes.  Thus  the 
current  entering  the  furnace  by  the  electrodes  AA,  will  pass  down 
to  the  bottom  of  the  furnace  and  pass  up  again  by  the  electrodes 
BB  and  CC.  This  arrangement  will  save  both  the  cost  of  the 
return  cables  and  the  electrical  energy  wasted  in  them.  It 
might,  however,  be  desirable  to  use  a  single  return  cable  between 
a  b  c  and  D  to  provide  for  any  unbalanced  current,  as  in  the 


Fig.  34. 


Fig.  35. 


operation  of  replacing  one  of  the  electrodes.  When  the  furnace 
is  once  in  regular  operation  the  current  will  be  carried  from  one 
electrode  to  another  through  the  molten  iron  in  the  smelting 
channel,  without  needing  to  pass  into  the  carbon  bottom  of  this 
channel,  and  the  carbon  bottom  might  therefore  be  omitted.  In 
a  furnace  using  three-phase  current,  as  represented  in  Figs.  34 
or  35,  a  small  proportion  of  the  current  will  pass  from  A  to  B, 
or  from  B  to  C,  directly  through  the  charge  without  passing 
through  the  molten  metal  or  the  bottom  of  the  furnace.  In 
these  furnaces  the  voltage  between  A  and  B,  or  between  B  and 
C,  will  be  1.73  times  the  voltage  between  A  and  a,  or  between 
B  and  b;  and  if  the  moveable  electrodes  were  near  together,  sur- 
rounded by  a  deep  layer  of  charge,  and  raised  considerably  above 
the  bottom  of  the  furnace,  the  bulk  of  the  current  might  pass 
directly  between  them,  and  the  metal  in  the  bottom  of  the 
furnace  might  become  too  cold  or  even  solidify.  In  the 
Turnbull  furnace,  Fig.  33,  there  would  be  no  danger  of 
this  as  the  electrodes  are  widely  separated  from  each 


I2O  THE     ELECTRIC     FURNACE. 

other,     and    are    not     raised     very     high     above     the     metal     in 
the    furnace. 

The  upper  part  of  the  furnace,  Fig.  33,  is  designed  to  utilize 
the  combustible  furnace  gases  for  preheating  the  ore  and  lime- 
stone. This  cannot  be  done  in  the  main  shaft  of  the  furnace,  for 
if  air  were  introduced  there  to  burn  the  gas,  it  would  also  burn 
the  charcoal  or  other  fuel  in  the  ore  mixture.  A  lateral  rotating 
tube,  T  T,  is  therefore  provided,  down  which  the  ore  gradually 
passes.  The  combustible  gases  from  the  furnace  burn  in  this 
tube,  air  being  introduced  through  the  bent  pipe  P  ;  and  the  pro- 
ducts of  combustion  escape  by  the  flue  F.  The  charcoal  or  other 
fuel  is  introduced  through  the  hopper  H,  and  is  thus  protected 
from  the  burning  gas  and  air. 

The  preheating  of  the  ore  and  limestone  in  the  tube  T  T,  has 
several  advantages.  It  calcines  the  limestone,  removing  the  car- 
bon dioxide  which  would  otherwise  rob  carbon  from  the  fuel ;  it 
roasts  the  ore,  removing  a  part  of  any  sulphur  it  may  contain  and 
leaving  it  in  a  better  condition  for  the  smelting  operation  ;  and 
the  ore,  by  being  heated,  is  fitted  for  immediate  reduction  to  the 
metallic  state  when  it  enters  the  reducing  atmosphere  of  the 
furnace,  as  well  as  gaining  an  amount  of  heat  which  would  other- 
wise have  to  be  furnished  by  the  electric  current.  This  pre- 
heating of  the  ore,  is  not  of  great  importance  in  a  blast  furnace, 
where  an  ample  supply  of  heat  is  carried  up  by  the  blast  and 
serves  to  preheat  an  immense  volume  of  ore  to  an  increasingly 
high  temperature  as  it  descends  in  the  furnace ;  but  in  the  electric 
furnace  only  a  small  amount  of  heated  gas  rises  from  the  smelt- 
ing zone  to  heat  the  descending  ore,  and  the  preheating  of  the 
ore  is  therefore  very  desirable. 

In  the  figure,  the  electrodes  are  shown  hanging  freely  in  the 
furnace,  but  it  is  intended  to  have  some  form  of  stuffing-box  to 
prevent  the  escape  of  gas.  Each  electrode  would  also  need  to 
be  insulated  from  the  metal  casing  of  the  furnace.  The  neces- 
sary supports  and  gearing  for  the  tube,  T  T,  are  omitted  in  the 
drawing.  The  metal  and  slag  are  drawn  off  through  suitable 
spouts  which  are  shown. 

A  3,000  horse-power  furnace*  of  this  type  is  in  course  of 
erection  at  Welland,  Ontario,  on  a  piece  of  ground  facing  the 
Welland  Canal.  It  is  expected  to  produce  35  tons  of  pig  iron  per  day 
when  the  ore  is  charged  cold,  or  40  tons  when  the  preheating  ar- 
rangement is  used.  Three  750  K.W.  transformers  will  be  employed 

*IIaanel    Report,    1907,    pp.    147-148. 


IRON     AND     STEEL.  121 

to  change  the  current  from  the  12,000  volts  of  the  supply  to  the 
30  or  40  volts  required  by  the  furnace.  Regulation  within  these 
limits  can  be  effected  by  taps  on  the  secondary  windings. 

The  furnace  is  intended  to  demonstrate  the  commercial  pos- 
sibility of  the  electric  smelting  of  Canadian  iron  ores,  even  at  a 
place  where  the  cost  of  power  is  not  very  low,  and  where  the 
ore  has  to  be  carried  at  least  150  miles.  Ores  from  Port  Arthur 
containing  i}4%  of  sulphur,  and  other  refractory  Canadian  ores 
will  be  used  in  order  to  demonstrate  the  possibility  of  electric 
smelting  under  these  conditions.  A  second,  larger  furnace,  and 
a  Heroult  furnace  for  the  manufacture  of  high  grade  steel  cast- 
ings, are  also  contemplated. 

A  2,000  horse-power  furnace*  of  similar  type  has  been 
•erected  at  Baird,  California,  for  smelting  a  rich  magnetite  ore 
with  charcoal.  The  furnace  has  a  guaranteed  output  of  20  tons 
a  day,  and  if  successful  the  plant  is  to  be  enlarged  to  a  capacity 
of  600-800  tons  per  day.  The  location  is  favorable  for  electric 
smelting  on  account  of  the  abundant  water  power  and  the  high 
price  of  pig  iron,  and  of  fuel  suitable  for  use  in  the  blast-furnace. 
The  furnace  was  formally  started  on  the  4th  of  July  before  the 
electrical  equipment  was  thoroughly  completed.  It  has  made 
iron,  seven  tons  being  drawn  on  the  i7th  July,t  but  for  steady 
work  more  electric  power  is  required  and  will  soon  be  supplied. 
Information  with  regard  to  the  furnace  is  given  in  the  Mining 
and  Scientific  Press  of  July  2oth,  and  in  the  Electrochemical  In- 
dustry, vol.  v.,  p.  318,  from  which  the  following  particulars  are 
taken: — The  ore  is  a  magnetite  containing  about  70.2%  Fe. , 
0.012%  S.,  0.01%  P.,  2.4%  SiO2,  and  insoluble.  Good  lime- 
stone for  flux  is  also  available.  The  ore  is  expected  to  cost 
$1.50  per  ton  delivered  to  the  smelter,  and  the  electric  power  will 
cost  $12  per  horse-power-year.  The  best  pig.  iron  sells  at  $30 
or  $32  per  ton  in  San  Francisco,  and  it  is  expected  that  the 
electric  pig  iron  can  be  made  and  delivered  there  at  a  cost  of 
from  $15  to  $18  per  ton.  In  this  furnace  there  are  three 
•electrodes  which  are  supplied  with  three-phase,  Go-cycle  current 
at  50  volts ;  the  amount  of  current  used  being  stated  as  30,000 
rimperes. 

Possibilities  in  electric  smelting.  Many  experiments  on  the 
electric  smelting  of  iron  ores  have  been  made  at  Sault  Ste.  Marie 
and  elsewhere,  but  they  have  all  been  hampered  by  inadequate 
electrical  equipment,  by  the  small  scale  of  the  furnace,  and  by 


*Dr.    Haanel,    Report,    1907,   p.    148. 

•f-Engineering   and  Mining  Journal,  August  loth,   1907,  p.  278. 


122 


THE    ELECTRIC     FURNACE. 


ORE   & 
LIMESTONE 


Escaping 
Gases 


•j,0,  ,  CaC03       N, 
Ox,  A1X03       H  - 


etc. 


Ore  is  dried  &  heated 
Limestone  is  calcined 


Heat  produced 
by  "burning-  CO 


CaO 


"1 


CO 


Heated  ore  is 
partly  reduced 
by  CO 


FeO  CaO 


CO 


Reduction  of  ore 
to  metal  by  C. 


Electrical 
Heating 


Molten    Slag  C    SiO*    CaO 


CaC03  =  CaO 


CO  •»•  0  = 


CO  =  2FeO 


FeO  +  C  =  Fe  +  CO 

L  +  ZC  •.  Si  +  8CO 


H  =  0.24  C  Rt 


L_J I 


Molten  Pig  (   Fe     C     Si    etc.\ 


Fig.  36.— Ideal  Furnace. 


IRON     AND     STEEL.  1 23 

the  fact  that  no  use  was  made  of  the  escaping  furnace  gases.  It 
is  very  desirable  to  know  what  improvement  in  efficiency  may  be 
expected  when  all  possible  improvements  have  been  made  in  the 
design  and  construction  of  the  electric  smelting  furnace,  and  what 
is  the  minimum  amount  of  fuel  and  electrical  energy  that  will 
then  be  needed.  For  this  purpose  the  operation  of  an  ideal 
furnace  may  be  studied,  omitting  for  the  present  any  considera- 
tion of  how  such  a  furnace  could  actually  be  constructed. 

The  ideal  furnace  shown  in  Fig.  36,  consists  of  a  smelting 
shaft  divided  by  imaginary  planes,  aa,  and  bb,  into  three 
distinct  zones,  A,  B,  and  C.  The  ore  and  limestone  are  intro- 
duced at  the  top  of  the  shaft  and  are  roasted  and  preheated  by  the 
gases  leaving  the  zone,  B,  which  are  burned  in  C,  by  air  intro- 
duced at  bb.  In  the  zone  B,  the  roasted  and  preheated  ore  is 
partly  reduced  by  the  reducing  gases  leaving  the  zone,  A,  enough 
combustible  gas  being  left  to  preheat  the  ore  in  C.  In  the 
lowest  zone,  C,  carbonacious  fuel  introduced-  at  aa,  serves  to 
complete  the  reduction  of  the  ore  to  the  metallic  state,  generating 
at  the  same  time  reducing  gases  which  pass  up  the  furnace,  and 
to  carburize  the  resulting  iron  ;  while  the  necessary  heat  is  pro- 
duced by  electrical  energy  introduced  for  example  by  the  elec- 
trodes, E  E.  The  figure  merely  serves  to  show  the  principles 
of  an  ideal  furnace  as  clearly  as  possible,  any  actual  furnace  em- 
bodying these  principles  would  be  constructed  quite  differently. 

It  is  well  known  that  in  the  iron  blast  furnace  the  efficiency  is 
limited  by  the  composition  of  the  escaping  gases,  at  least  half 
the  carbon  that  is  burnt  in  the  furnace. escaping  in  the  half-con- 
sumed form  of  carbon  monoxide.  The  same  is  true  of  any  simple 
electric  smelting  furnace,  such  as  Heroult's  experimental  furnace 
in  which  the  charcoal  was  introduced  with  the  ore  at  the  top 
of  the  furnace.  If  now  the  carbon  monoxide  escaping  from 
such  a  furnace  is  burnt  and  used  to  preheat  the  ore,  a  certain 
saving  of  electrical  energy  would  be  obtained,  but  there  would 
be  no  saving  of  fuel,  and  the  burning  of  the  waste  gases  would 
sometimes  furnish  more  heat  than  was  needed  for  preheating  the 
ore,  thus  leading  to  waste  and  overheating  of  the  top  of  the 
furnace.  In  the  ideal  furnace  of  Fig.  36,  part  of  the  waste  gases 
are  Used  for  a  partial  reduction  of  the  ore  in  zone  B,  and  the  re- 
mainder is  employed  for  preheating  in  zone  C.  In  this  way  the 
greatest  possible  economy  in  both  fuel  and  electrical  energy  can 
be  obtained.  As  the  fuel  is  used  in  this  furnace  both  for  reduc- 
tion and  for  heating,  it  will  be  possible,  within  certain  limits,  to 
use  rather  more  fuel  and  less  electrical  energy,  or  less  fuel  and 


124  THE     ELECTRIC     FURNACE. 

more  electrical  energy,  obtaining  in  both  cases  perfect  combus- 
tion and  economy,  and  the  relative  price  of  the  two  commodities 
would  decide  which  to  employ. 

A  simple  example  will  demonstrate  the  action  of  the  furnace. 
Suppose  that  pure  hematite  ore,  Fe2C>3  is  charged  in  at  the  top 
of  the  furnace  and  that  pure  carbon  equal  to  15%  of  the  weight 
of  the  ore,  (two  atoms  of  carbon  to  each  molecule  of  ferric  oxide), 
is  charged  at  aa,  together  with  as  much  additional  carbon  as  is 
needed  to  carburize  the  iron.  The  ore,  preheated  in  C,  will  be 
reduced  to  FeO  in  B,  and  in  A,  the  FeO  will  be  reduced  to 
metallic  iron.  The  equations  show  how  this  works  out,  and 
that  on  entering  C,  half  of  the  carbon  will  have  been  fully  burnt, 
and  half  will  be  in  the  form  of  carbon  monoxide. 

In  A, 
In  B, 
In  C, 

The  heat  value  of  the  carbon  monoxide  burning  in  C,  is  35% 
of  the  original  heat  value  of  the  carbon,  and  this,  with  the  heat 
carried  up  by  the  furnace  gases  would  heat  the  ore  to  about 
^,5oo°C.,  which  would  be  needlessly  high.  If  on  the  other  hand 
the  carbon  were  reduced  to  about  11%  of  the  ore  (three  atoms 
ol  carbon  to  two  molecules  of  ferric  oxide)  the  whole  of  the 
carbon  would  be  required  for  reduction,  leaving  nothing  for  pre- 
heating. Deciding  on  some  proportion  of  carbon  between  11% 
and  15%  of  the  ore,  it  would  be  possible  to  calculate  how  much 
electrical  energy  would  be  needed  to  supply  the  remainder  of  the 
heat  for  smelting. 

In  the  experiments  that  have  been  made  in  electric  smelt- 
ing, non-volatile  fuel  such  as  coke  or  charcoal  has  been  em- 
ployed, because  the  volatile  matter  arising  from  a  fuel  like  soft 
coal  would  not  only  be  wasted  but  would  have  made  the  opera- 
tion of  the  furnace  decidedly  unpleasant.  In  the  ideal  furnace, 
ample  provision  is  made  for  the  use  of  carbonacious  gases  in  the 
zones  B  and  C,  and  any  kind  of  fuel,  even  oil  or  natural  gas, 
could  be  used  effectively  if  introduced  at  the  point  aa. 

The  fuel  entering  the  ideal  furnace  is  completely  burnt  be- 
fore it  leaves  the  furnace,  and  the  whole  value  of  it  and  of  the 
electrical  energy  may  be  communicated  to  the  charge.  The 
fuel  is  used  in  part  for  the  chemical  work  of  reducing  the  oxides 
to  metal  and  carburizing  the  resulting  iron,  and  the  heat  from 
the  remainder  of  the  fuel  and  from  the  electrical  energy  is  used 
in  part  to  furnish  heat  for  the  chemical  changes  that  must  be 


IRON     AND     STEEL.  125 

effected  in  the  ore,  and  in  part  leaves  the  furnace  in  the  molten 
metal  and  slag,  in  the  gases  escaping  from  the  top  of  the  furnace, 
and  by  conduction  through  the  walls  of  the  furnace.  The  heat 
consumed  in  chemical  reactions  is  an  essential  part  of  the  opera- 
tion, the  heat  carried  out  by  the  molten  slag  and  metal  is  usually 
considered  to  be  an  unavoidable  loss,  though  some  of  this  might 
be  recovered  if  it  were  worth  while,  the  heat  escaping  in  the 
gases  at  the  furnace  top  may  be  reduced  to  a  very  small  pro- 
portion of  the  whole,  and  the  loss  by  conduction  through  the 
walls  can  be  reduced  to  a  moderate  proportion  in  well  built 
furnaces  of  large  dimensions. 

A  few  examples  will  now  be  given  to  show  what  will  be  the 
minimum  amount  of  fuel  and  electrical  energy  needed  for  smelt- 
ing an  iron  ore  in  such  a  furnace. 

The  first  example  is  one  given  by  Prof.  Richards*  and 
shows  how  much  electrical  energy  and  good  charcoal  would  be 
needed  to  smelt  a  magnetite  ore,  obtaining  a  gray  pig  iron. 

The  magnetite  ore  contains : — 

Per  Cent.  Per  Cent. 

Fe2O3      60.74  ^IgO      5-5° 

FeO      17. 18  P2O5       0.04 

SiO2       6.60  S       0.57 

A12O3      i^j.8  CO2 2.05 

CaO       2%4  H2O       3.00 

,It  is  to  be  mixed  with  a  good  variety  of  charcoal,  assumed 
90%  carbon  and  10%  moisture,  and  with  enough  pure  silica  sand 
to  make  a  slag  with  33%  silica.  The  pig  iron  is  to  contain  4% 
carbon,  3.5%  silicon,  and  92.4%  of  iron.  One  ton  of  pig  iron 
will  require  1.654  tons  of  iron  ore  for  its  production.  Taking 
first  the  case  in  which  the  gases  entering  zone  C,  contain  two 
volumes  of  CO2  to  one  volume  of  CO.  The  carbon  needed  for 
one  metric  ton  of  pig  will  be  224  kilograms ;  that  is  249  kilo- 
grams, or  550  Ibs.  of  charcoal.  The  electrical  energy  required 
will  depend  upon  how  much  heat  is  lost  by  conduction  and  radia- 
tion from  the  furnace,  and  in  the  escaping  gases.  Supposing 
first  that  the  gases  are  quite  cold,  and  that  no  heat  is  lost  by 
radiation,  etc.,  the  electrical  energy  needed  would  be  about  0.13 
horse-power-years  per  metric  ton  of  pig,  while  if  the  more 
reasonable  assumption  were  made  that  the  gases  escaped  at 
3oo°C.,  and  that  the  losses  by  conduction  and  radiation  from  the 

'Richards   Metallurgical  Calculations,   vol.    ii.,    Problem    76,   p.   404. 


126  THE  ELECTRIC  FURNACE. 

furnace  were  20%  of  the  heat  generated,  (that  is  of  the  electrical 
heat  and  of  the  heat  produced  by  the  gases  burning  in  the  zone 
C),  0.20  horse-power-years  of  electrical  energy  would  be  needed. 
In  this  case  the  heat  produced  in  C  by  burning  gases  was  about 
30%  of  the  heat  produced  electrically.  It  would  be  possible  to 
use  rather  less  charcoal  and  more  electrical  energy,  or  less 
electrical  energy  and  more  charcoal  than  indicated  in  this  ex- 
ample, but  taking  these  figures  as  fairly  typical  of  the  amount  of 
good  charcoal  and  of  electrical  energy  actually  employed  in  the 
furnace,  it  will  be  necessary  to  make  certain  additions  if  the  re- 
sults are  to  represent  working  conditions.  Thus  to  the  electrical 
energy  must  be  added  the  losses  in  transformers,  cables  and 
connections,  say  10%,.  raising  the  figure  to  0.22  horse-power-years, 
and  a  further  addition  must  be  made  to  allow  for  the  fact  that 
the  furnace  will  not  be  operated  continuously  during  the  year, 
and  that  even  when  it  is  running  it  wrill  not  always  draw  the  full 
power  for  which  payment  is  made.  In  this  connection  it  will 
not  be  necessary  to  consider  the  time  when  the  furnace  may 
be  out  of  work  for  long  periods  for  repairs,  as  provision  would 
be  made  by  having  a  spare  furnace,  to  employ  the  power  as 
regularly  as  possible.  A  certain  loss  of  charcoal  will  occur 
through  mechanical  losses,  and  it  will  probably  be  safe  to  allow 
600  Ibs.  of  charcoal  and  0.25  E.H.P.  years  per  ton  of  pig  iron 
as  the  final  solution  of  the  above  problem. 

As  another  example  may  be  taken  the  i3th  experimental 
run  with  the  Heroult  furnace  at  Sault  Ste.  Marie  in  February, 
1906.*  The  run  lasted  61 J^  hours,  the  mean  current  was  5,000 
amperes  at  35.7  volts,  with  a  power  factor  of  0.919,  giving  164 
as  the  mean  kilowatts  during  the  run.  12,858  Ibs.  of  pig  iron 
were  obtained  with  a  consumption  of  1,140  Ibs.  of  charcoal  and 
0.268  E.H.P.  years  per  ton  of  pig. 

The  ore  was  magnetite  from  Wilbur  mine,  containing: — 

SiO2—  6.20%  AbO3— 2.56%  P^S— 0.023% 

Fe203— 55.42%  CaO— 2.00%  (P— 0.01%) 

FeO— 23.04%  MgO— 6.84%  S— 0.05% 

(Fe— 56.69%)  MnO— 0.26%  CO2,  etc.— 3.61% 

The  charcoal  contained,  14.0%  moisture,  27.56%  volatile 
matter,  55.9%  fixed  carbon,  2.54%  ash,  and  0.058%  sulphur. 


*Dr.    Haanel,  1907  Report,   p.    46.      The    figures    in    the  Report    refer    to   the   2,000   Ib. 

ton  of   pig  iron.  In   this   book   the   author   has   adopted   the   long  ton  of   pig   iron,   and 

occasionally    the  metric    ton    which    is    almost    identical,    as    agreeing    more    generally 

\vith    commercial  practice. 


IRON     AND     STEEL.  1 27 

During  the  run  21,150  Ibs.  of  ore  were  smelted  with  6,555 
Ibs.  of  charcoal,  and  1,191  Ibs.  of  sand  for  flux.  The  sand  con- 
tained 81.71%  of  silica,  and  14.27%  of  alumina,  with  1.6%  of 
lime  and  i.n%  of  magnesia. 

The  mean  analysis  of  the  pig  iron  was : — 

Si,  1.75%;  S,  0.029%;  P,  0.022%;  Mn,  0.23%;  C,  4.58%. 

Supposing  that  the  ore  were  smelted  in  a  simple  furnace 
such  as  was  actually  used,  in  which  the  ore,  flux  and  charcoal 
are  all  charged  into  the  furnace  at  the  top,  and  no  use  is  made 
of  the  escaping  gases,  it  will  be  necessary  to  make  some  assump- 
tion in  regard  to  the  composition  of  these  gases  as  no  informa- 
tion is  given*  Assuming  that  they  consisted  of  equal  volumes 
of  CO  and  CO2,  it  will  be  found  that  the  carbon  required  to  re- 
duce the  ore  and  carburize  the  pig  iron  will  be  14%  of  the  ore, 
which  will  correspond  to  25%  of  charcoal,  or  930  Ibs.  of  charcoal 
per  ton  of  pig.  In  the  actual  case  1,140  Ibs.  were  used,  part  of 
which  wras,  however,  burned  on  the  top  of  the  charge.  Assum- 
ing further  that  the  gases  escape  at  4oo°C,  and  that  20%  of  the 
electrical  heat  is  wasted  by  radiation  and  conduction  from  the 
furnace,  a  calculation  showed  that  0.267  E.H.P.  years  per  ton 
of  iron  would  be  needed,  a  figure  which  agrees  better  than  could 
be  expected  with  the  amount  actually  used,  which  was  0.268. 

If  now  the  same  charge  were  smelted  in  the  ideal  furnace, 
so  that  the  escaping  gases  were  utilized  to  preheat  the  charge, 
and  allowing  for  the  loss  of  20%  of  the  electrical  heat  and  20%  of 
the  heat  produced  by  the  burning  gases,  it  will  be  found  that 
only  0.216  E.H.P.  years  would  be  needed. 

In  this  calculation  only  the  fixed  carbon  in  the  charcoal  has 
been  considered,  but  with  the  ideal  furnace  the  volatile  matter  in 
the  charcoal  would  also  be  of  use  for  reducing  and  preheating 
the  ore  in  the  upper  zones  of  the  furnace.  A  smaller  amount  of 
charcoal  and  electrical  energy  would  therefore  be  sufficient. 

In  conclusion  it  may  be  stated  that  in  an  electric  furnace  of 
good  construction,  one  ton  of  pig  iron  should  be  obtained  with 
the  use  of  600  to  800  Ibs.  of  charcoal  and  about  0.20  to  0.22 
E.H.P.  years,  and  that  in  order  to  allow7  for  delays  the  amount 
of  electrical  energy  should  be  raised  to  about  0.25  E.H.P.  years. v 
The  only  furnace  illustrated  in  these  pages  in  which  the 
escaping  gases  are  used  to  preheat  the  charge  is  the  TurnbuJI 
furnace,  Fig.  33.  The  main  part  of  this  furnace  corresponds  to 

*These  figures  apply  to  ores  of  50  per  cent,  or  60  per  cent,  of  iron.  For  poorer 
ores  a  larger  amount  of  electrical  energy  would  be  needed,  but  the  amount  of  char- 
coal per  ton  of  pig  would  not  be  much  increased. 


128  THE     ELECTRIC     FURNACE. 

zone  A  of  the  ideal  furnace  and  the  preheating  tube  to  zone  C. 
There  is  thus  nothing  corresponding  to  zone,  B,  in  which  the 
gases  from  the  lower  part  of  the  furnace  can  exercise  their  reduc- 
ing action  on  the  preheated  ore.  It  remains  to  be  seen  whether 
this  zone  will  be  required  in  practice. 

After  devising  the  ideal  furnace  of  Fig.  36,  in  which  the 
greatest  advantage  is  taken  of  the  fuel  and  of  the  electrical 
power,  the  author  found  that  it  had  already  been  invented  and 
patented  by  Paul  Heroult,*  who  introduces  the  air  by  tuyeres 
at  bb,  and  supplies  the  fuel  by  a  vertical  tube  down  the  centre 
of  the  furnace  to  the  level  aa. 

Collecting  the  results  that  have  been  obtained  in  the  electrical 
production  of  pig  iron  from  the  ore,  it  may  be  stated  that  the 
process  is  technically  successful,  and  gives  better  results  than 
the  blast  furnace  in  regard  to  the  use  of  sulphurous  ores,  titani- 
ferous  anJ  similar  refractory  ores  and  ores  in  a  state  of  powder, 
such  as  iron  sand  or  ores  which  have  been  concentrated  by 
magnetic  or  similar  processes.  The  process  also  allows  of  the 
use  of  inferior  and,  therefore,  cheaper  fuel.  The  power  re- 
quired is  about  y£  of  a  horse-power  year,  depending  on  the 
richness  of  the  ore.  The  fuel  used  for  reducing  and  carburiz- 
ing  the  iron  is  600  or  800  Ibs.  of  coke  or  charcoal,  which  need 
not  be  of  good  quality. 

Comparing  the  cost  of  smelting  by  the  two  processes,  apart 
from  considerations  of  scale  working,  which  will  at  first  greatly 
hamper  any  electric  smelting  project,  the  main  items  of  cost  to 
compare  are  the  fuel  and  the  electric  power.  Thus  in  the 
electric  furnace  the  ton  of  pig  iron  would  require,  at  present, 
y±  horse-power  year,  and  600  or  800  Ibs.  of  coke  or  charcoal, 
while  the  blast  furnace  would  require  some  1,900  or  2,000  Ibs. 
of  coke  for  pure  and  easily  reducible  ores,  and  as  much  as  2,500 
Ibs.  or  3,000  Ibs.  when  poor  ores  and  coke  are  used.  Balancing 
the  cost  of  }^  horse-power  year  against  the  cost  of  the  coke  that 
is  saved,  will  give  a  general  idea  of  the  prices  of  coke  and  power 
which  would  permit  of  electric  smelting.  Of  the  other  expenses 
of  the  two  methods,  the  electric  furnace,  receiving  high  voltage 
current  at  a  certain  price,  would  require  transformers  and  heavy 
cables  from  these  to  the  furnace.  The  carbon  electrodes  must 
also  be  supplied.  The  blast  furnace,  on  the  other  hand,  has 
the  expense  of  the  blowing  engines  with  their  attendant  boilers, 
and  of  the  enormous  hot  blast  stoves  for  preheating  the  blast. 


*P.  L.  T.    Heroult.     Apparatus   for   smelting   iron  ore.     IT.   S.    patent  815,293,   March, 
1906.      Electrochemical     Industry,    vol.    iv.,    1906,    p.    152. 


IROX     AND     STEEL.  129 

The  furnaces  constructed  by  Heroult  and  by  Keller  are  so 
very  small  in  comparison  with  a  modern  blast  furnace  that  the 
general  expenses  would  tell  very  much  more  heavily  on  the 
electric  process.  These  furnaces  moreover  need  a  number  of  im- 
provements before  they  reach  their  most  satisfactory  and 
economical  design.  These  improvements  will,  no  doubt,  ac- 
company a  gradual  increase  in  size,  and  the  electric  smelting  of 
iron  ores  will  probably  become  a  commercial  fact  in  localities 
favorable  to  its  operation. 

III.— The  Direct  Production  of  Steel  from  Iron  Ore. 

It  is  quite  possible  to  produce  malleable  iron  or  steel  directly 
from  the  ore,  by  heating  the  ore  with  a  limited  amount  of  carbon ; 
enough  carbon  being  provided  to  reduce  the  oxide  of  iron  to  the 
metallic  state,  but  not  enough  to  leave  any  excess  of  carbon, 
which  would  unite  with  the  reduced  metal  to  make  pig  iron. 
The  primitive  metallurgists  obtained  wrought  iron  and  steel  in 
this  manner,  by  reducing  the  ore  in  small  furnaces,  instead  of 
first  making  pig  iron  and  then  turning  the  pig  iron  into  wrought 
iron  or  steel  as  is  the  present  practice.  Iron,  nearly  free  from 
carbon,  is,  however,  very  difficult  to  melt,  and  in  the  little  forge 
or  furnace  of  the  savage  the  iron  was  not  melted,  but  obtained 
in  the  form  of  a  solid  lump,  which  was  then  cut  up  and  ham- 
mered into  shape ;  it  being  often  necessary  to  pull  the  furnace 
down  in  order  to  extract  the  bloom  of  reduced  iron  or  steel. 
With  larger  blast  furnaces  it  is  possible  to  melt  even  pure  iron, 
but  the  melted  iron  will  rapidly  absorb  carbon  from  the  fuel 
employed,  and  so  will  become  pig  iron.  It  follows  from  this 
and  other  reasons,  that  wrought  iron  and  steel  cannot  be  made 
in  a  blast  furnace.  In  the  electric  smelting  furnace,  however, 
the  conditions  are  different,  because,  as  the  heat  is  supplied 
electrically  and  is  not  dependent  upon  the  burning  of  fuel,  the 
amount  of  carbon  supplied  can  be  adjusted  exactly  to  suit  the 
chemical  needs  of  the  ore,  so  as  to  make  a  carbon — free  iron, 
or  any  desired  grade  of  steel. 

Captain  Stassano  has  effected  this  in  his  electric  arc 
furnace*  (Fig.  37),  which  resembles  an  open-hearth  steel  furnace, 
in  which  the  flame  of  burning  gas  has  been  replaced  by  the  flame 
of  the  electric  arc.  The  furnace  consists  of  an  iron  casing  lined 
with  fire-brick,  E,  and  with  an  inner  lining  of  magnesite  bricks, 

*Electrochem.    Industry,    vol.    i.,    pp.    247,   363,   and   461  ;   vol.    iii.,   p.    391. 
Engineering  and  Mining  Journal,  June  isth,  1907,  p.   1135. 


1 3o 


THE    ELECTRIC     FURNACE. 


D.  An  arc  is  maintained  between  the  ends  G  and  H  of  two, 
nearly  horizontal  carbon  electrodes,  the  holders  of  which  work 
through  air-tight  stuffing  boxes  in  water-cooled  casings,  J  and 
K.  This  arrangement  prevents  the  escape  of  the  furnace  gases, 
cools  the  electrode  holders  and  prevents  the  oxidation  of  the  ex- 
ternal portions  of  the  electrodes.  The  necessary  amount  of 


Fig.  37. — Stassano  Furnace. 

carbon  for  making  iron  or  steel  is  incorporated  with  the  ore  in 
the  form  of  briquettes,  which  are  introduced  into  the  furnace, 
and  heated  until  the  chemical  reactions  have  taken  place  and  the 
reduced  metal  has  melted.  The  metal  and  slag  are  then  tapped 
out  and  the  operation  is  repeated.  The  carbon  monoxide,  re- 
sulting from  the  reaction  of  the  carbon  and  the  ore,  escapes 
from  the  furnace  by  the  hole  F.  This  waste  gas  might  be  em- 
ployed for  drying  and  preheating  the  ore. 

Dr.  Haanel  was  unable  to  see  Stassano's  furnace  at  Turin, 
in  operation,  as  it  was  out  of  repair  at  the  time  of  his  visit,  but 
he  gives  a  description  of  the  furnace  and  prints  an  account  of 
the  process  written  by  the  inventor.*  The  newer  forms  of 
furnace  are  inclined  about  7°  from  the  vertical  and  rotate  slowly 
round  this  inclined  axis,  with  a  view  to  stirring  up  the  charge 
and  allowing  the  heat  of  the  arc  to  act  more  freely  on  the  ore. 
In  some  furnaces  three  electrodes  are  used,  with  three-phase 
current,  while  in  other  furnaces  four  electrodes  are  employed. 
Stassano  gives  the  following  particulars  with  regard  to  a  furnace 


*Haanel,    European   Report,    1904,    pp.    178-214. 


IRON*     AND     STEEL.  131 

of  1,000  horse-power.*  The  cost  of  the  furnace  is  $5,000,  the 
output  per  day  is  4  or  5  tons,  a  current  of  4,900  amperes  at  150 
volts  is  distributed  to  four  electrodes  (2,450  amperes  to  each 
electrode)'.  The  electrodes  are  6  inches  in  diameter  and  4  feet 
to  5  feet  long.  A  five  foot  electrode  weighs  130  Ibs.,  and  costs 
~  cents  a  Ib.  The  consumption  of  electrodes  is  22  to  33  Ibs.  per 
ton  of  product,  that  is  70  cents  to  $i  per  ton  of  steel.  The 
lining  is  of  magnesite  bricks,  and  two  days  are  required  for  re- 
pairing the  furnace.  The  lining  will  last  at  least  40  days.  One 
man  is  needed  per  furnace  to  regulate  the  arc ;  one  man  for 
charging  two  furnaces,  and  five  men  for  tapping  six  furnaces. 
Taking  the  above  figures  of  1,000  E.H.P.  days  for  4  or  5  tons 
of  iron  or  steel,  each  ton  would  need  0.55  to  0.69  horse-power 
years  for  its  production.  Dr.  Goldschmidtt  investigated  the 
process  in  1903  on  behalf  of  the  German  patent  office,  and  found 
that  it  was  technically  successful,  making  workably  ductile 
iron  with  less  than  0.2%  of  carbon  directly  from  pure  Italian 
ores.  The  energy  used  was  0.46  to  0.49  horse-power  years 
per  metric  ton  of  iron.  The  process  was  reported  as  too 
expensive  to  compete  with  existing  methods  in  Ger- 
many. 

Comparing  the  direct  process  of  Stassano  with  the  more 
usual  plan  of  smelting  first  to  pig  iron,  and  then  refining  the 
iron  and  making  steel ;  it  will  be  seen  that  the  electrical  energy 
needed  to  smelt  ore  directly  to  steel  in  the  Stassano  furnace  is 
greater  than  the  energy  needed  for  the  other  two  processes,  and 
that  his  process  was  only  used  with  pure  ores ;  while  the  indirect 
method  allows  of  the  use  of  any  kind  of  iron  ore.  The  Stassano 
furnace  is  intermittent  in  action,  as  each  charge  of  ore  must  be 
reduced,  melted  and  tapped  before  a  fresh  one  can  be  intro- 
duced. Moreover  the  economy  of  heat  is  poor  because  the 
heat  of  the  escaping  gas  is  not  utilized,  and  its  chemical 
energy  is  not  employed,  as  it  might  be,  for  the  reduction  or  pre- 
heating of  the  ore. 

The  shaft  furnace  must  always  be  more  efficient  than  a 
furnace  like  Stassano's ;  but  if  it  were  found  possible  to  produce 
good  structural  steel  from  impure  ores,  in  an  electric  furnace 
of  this  type,  there  might  be  some  hope  of  its  commercial  success 
under  favorable  geographical  conditions.  Stassano  has  appar- 
ently always  used  pure  ores,  and  has  therefore  thrown  no  light 
on  this  point. 

*Haanel,   European   Report,   1904,   p.    12. 
•f-Electrochemical  Industry,  vol.  i.,  1903,  p.  247. 


13.2  THE     ELECTRIC     FURNACE. 

With  regard  to  the  possibility  of  producing  pure  steel  in  a 
single  operation  from  impure  ores,  the  conditions  under  which 
the  hurtful  elements  sulphur  and  phosphorus  are  removed  from 
iron  and  steel  may  be  considered.  In  the  blast  furnace,  sulphur 
is  removed  from  the  iron  and  passes  into  the  slag  as  calcium 
sulphide,  its  removal  in  this  way  being  more  complete  as  the 
furnace  is  more  strongly  reducing,  and  the  slag  is  richer  in 
lime ;  that  is  when  the  conditions  are  favorable  for  the  forma- 
tion of  calcium  to  combine  with  the  sulphur.  The  electric 
furnace  making  pig  iron  has  more  strongly  reducing  conditions, 
and  can  carry  more  lime  in  the  slag  than  is  possible  in  the  blast 
furnace ;  this  explains  its  superior  ability  to  eliminate  sulphur. 
When,  however,  the  ore  is  smelted  directly  to  steel  in  the  electric 
furnace,  the  conditions  are  far  less  reducing,  and  there  is  no 
reason  for  expecting  the  removal  of  sulphur  as  calcium  sulphide, 
even  in  the  presence  of  a  limey  slag.  In  the  open-hearth  furnace 
sulphur  can  be  removed  from  steel  by  the  action  of  a  basic  or 
limey  slag,  but  not  very  easily.  The  conditions  in  the  open- 
hearth  furnace  are  oxidizing  instead  of  reducing,  and  the  sulphur 
will  be  removed  as  calcium  sulphate.  In  the  electric  steel 
furnace  the  same  difficulty  may  be  expected  in  the  removal  of 
the  sulphur. 

With  regard  to  the  elimination  of  phosphorus  the  conditions 
are  quite  the  reverse,  as  this  element  can  only  be  removed  by 
oxidation.  In  the  blast  furnace  any  phosphorus  in  the  charge 
finds  its  way  into  the  pig-iron,  and  the  same  takes  place  in  the 
electric  furnace  making-  pig  iron  ;  but  in  the  open-hearth  furnace 
with  a  strongly  basic  slag,  the  removal  of  phosphorus  can 
be  satisfactorily  accomplished,  and  the  same  will  hold  good  in 
the  production  of  steel  directly  from  the  ore  in  the  electric 
furnace,  if  the  slag  is  limey  and  sufficiently  oxidizing. 

In  this  connection  some  laboratory  experiments  by  Mr.  J. 
W.  Evans  on  the  direct  production  of  steel  from  sulphurous  and 
and  titaniferous  ores  possess  more  interest  than  would  other- 
wise attach  to  smelting  experiments  on  so  small  a  scale.  From 
ore  containing  i%  of  sulphur,  Mr.  Evans  obtained  samples  of 
steel  containing  0.12%,  0.17%,  and  0.08%  of  sulphur.  These 
steels,  while  not  sufficiently  free  from  sulphur  for  commercial 
use,  show  a  considerable  removal  of  that  element,  but  as  the 
results  were  obtained  in  a  small  electric  crucible  holding  only 
an  ounce  of  ore,  it  seemed  doubtful  whether  they  could  be  de- 
pended on  to  be  repeated  on  a  larger  scale.  There  can  be 
little  doubt  that  in  an  electric  steel-making  furnace  such  as  the 


IRON     AND     STEEL.  133 

Heroult  or  the  Stassano  in  which  the  molten  steel  can  be  washed 
by  the  repeated  addition  and  removal  of  limey  slags,  any  sulphur 
and  phosphorus  can  ultimately  be  removed ;  but  as  the  produc- 
tion of  steel  directly  from  the  ore  can  be  accomplished  most 
economically  in  some  form  of  shaft  furnace,  that  is  a  furnace  re- 
sembling the  Heroult  ore-smelting  furnace,  which  is  operated 
continuously,  instead  of  intermittently  like  the  steel  furnaces. 
It  was  therefore  a  question  of  the  greatest  importance  in  re- 
gard to  the  possible  production  of  steel  directly  from  the  ore,  to 
determine  whether  in  a  continuous  smelting  furnace,  steel  free 
from  sulphur  and  phosphorus  could  be  produced  from  ores 
carrying  the  usual  proportions  of  these  elements.  The  experi- 
ments of  Mr.  Evans  could  not  be  taken  as  an  answer  to  this 
question  as  his  furnace  did  not  operate  continuously,  and  the 
conditions  were  decidedly  different  from  those  in  a  continuous 
furnace.  The  author  accordingly  proposed  the  problem  to  two 
of  his  students,  Messrs.  W.  G.  Brown  and  F.  E.  Lathe,  and 
embodied  the  results  of  their  work  in  a  paper  read  before  the 
Canadian  Mining  Institute  in  March,  1907.  The  experiments 
were  made  in  a  small  shaft  furnace  resembling  the  furnace  used 
at  Sault  Ste.  Marie,  but  lined  with  burnt  magnesite.  As  no 
carbon  could  be  used  as  a  lining  for  the  crucible  of  the  furnace, 
electrical  connection  was  made  by  means  of  an  iron  rod  passing 
through  the  bottom  of  the  furnace.  The  power  available  was 
rather  small,  but  it  was  found  possible  to  run  the  furnace  regu- 
larly for  a  few  hours  at  a  time,  producing  low-carbon  steel  of 
which  some  two  or  three  pounds  were  tapped  at  intervals  of  about 
half  an  hour. 

The  ore  used  was  a  pure  hematite  from  Lake  Superior, 
containing  97%  Fe2C>3,  2.23%  of  silica,  and  0.68%  of  alumina. 
Clay,  sand,  and  lime  were  added  to  make  a  slag  equal  to  about 
half -the  weight  of  the  resulting  metal,  and  i%  each  of  sulphur 
and  phosphorus  was  added  in  the  form  of  monosulphide  of  iron 
and  calcium  phosphate. 

Analyses  of  the  steel  and  slag  from  a  number  of  the  taps 
are  given  in  table  xiii.,  and  show  very  clearly  the  effect  of 
lowering  the  carbon  in  the  charge,  and  so  producing  steel  in- 
stead of  pig  iron.  If  sufficient  carbon  had  been  added  in  the 
charge,  a  pig  iron  would  have  been  produced  rich  in  carbon  and 
silicon,  low  in  sulphur,  and  with  more  than  i%  of  phosphorus. 
With  the  smaller  amount  of  carbon  which  was  charged  in  these 
experiments,  the  resulting  iron  contained  less  carbon  and  silicon 
and  more  sulphur,  (see  No.  i  in  the  table).  As  the  carbon  in 

10 


134  THE.   ELECTRIC     FURNACE. 

the  charge  was  diminished,  the  resulting  metal  contained  still 
less  carbon  and  silicon,  and  at  the  same  time  the  phosphorus  in 
the  steel  was  progressively  reduced,  until  in  the  lowest  carbon 
steels  the  phosphorus  became  low  enough  for  structural  pur- 
poses. The  sulphur,  on  the  other  hand,  which  would  have 
been  nearly  eliminated  in  the  production  of  pig  iron,  increased 
with  the  decrease  of  carbon,  no  doubt  because  there  was  less 
opportunity  for  its  removal  as  calcium  sulphide ;  but  further  de- 
crease of  carbon,  resulting  in  a  highly  oxidised  slag,  served  to 
remove  a  portion  of  the  sulphur,  probably  a  calcium  sulphate,  in 
the  same  way  that  it  is  removed  in  the  basic  open-hearth  furnace. 

TABLE   XIII. 
Steel  and  Slag  Analyses. 

%o/  o/  o/  o/  o/  o/ 

/o  /o  /o  /o  /o  /o 

Steel.  123456  7 

C       2.09       1.16         .54         .088         .088         .088  .091 

Si      20          .15          .24  

S     75         .91        1.04         .54  .65  .68  .47 

P       49         .24         .20         .039         .046         .081  .031 

O/  O/  O/  O/  O/  O/  O/ 

Slag. 
FeO 

Si02 

CaO 

MgO 
Al203 

The  first  three  analyses  are  taken  from  one  run  of  the 
furnace,  while  the  last  four  are  from  another  run,  in  which  less 
carbon  was  charged.  The  second  run  appears  to  show  that  the 
carbon  in  the  steel  could  be  lowered  to  about  0.09  per  cent.,  but 
that  any  further  reduction  in  the  amount  of  carbon  charged, 
merely  increased  the  already  large  percentage  of  iron  oxide  in 
the  slag,  without  lowering  any  further  the  carbon  in  the  steel. 
Mr.  Evans  appears  to  have  had  still  more  oxidising  conditions, 
reducing  the  carbon  in  his  steel  to  0.06  per  cent.,  with  a  cor- 
responding reduction  in  the  sulphur,  which  he  succeeded  in 
lowering  to  0.08  per  cent,  in  one  experiment.  The  lowest 
sulphur  in  the  present  series  of  experiments  was  0.34  per  cent. 

While  these  analyses  only  represent  the  result  of  smelting 
an  iron  ore  in  an  electric  furnace  with  particular  conditions  of 
charge,  shape  of  furnace,  current  density,  etc.,  and  changes  Fn 


I 

2 

3 

4 

5 

6 

7 

4-5 

7-i 

3-6 

20.54 

20.64 

26.94 

33  -46 

3J-7 

3°-3 

32.2 

16.77 

18.92 

15.66 

15.42 

30.7 

30.8 

36.0 

27.07 

35-1? 

35-1? 

32-54 

15.8 

21.3 

17.6 

22.34 

13.90 

13.84 

IJ-34 

13.2 

9-3 

11.7 

7.48 

5-30 

3-53 

2.13 

.         IRON     AND     STEEL.  1^5 

any  of  these  conditions  might  influence  the  composition  of  the 
resulting  steel,  they  indicate  pretty  clearly  that  in  the  electro- 
thermic  production  of  steel  directly  from  a  sulphurous  ore,  it 
will  not  be  easy  to  remove  the  sulphur  in  an  electric  furnace, 
operating  continuously  like  a  blast  furnace;  although  it  may  be 
possible  with  intermittent  operation,  as  in  an  electric  open- 
hearth  furnace.  Phosphorus,  on  the  other  hand,  can  be  satis- 
factorily removed  when  low  carbon  steel  is  produced. 

At  present  the  most  satisfactory  process  for  making  steel 
electrically  from  iron  ore,  is  to  smelt  electrically  to  pig  iron  in  a 
shaft  furnace,  thus  eliminating  the  sulphur ;  transfer  the  molten 
pig  to  an  electric  open-hearth  furnace  and  there  remove  the 
excess  of  carbon,  silicon,  etc.,  and  the  phosphorus.  If  the  shaft 
furnace  could  produce  a  nearly  pure  iron  directly,  so  that  the 
second  furnace  would  be  little  more  than  a  ladle  for  adjusting  the 
composition,  a  decided  economy  should  be  effected.  A  combina- 
tion of  electric  shaft  furnace  for  making  pig  iron,  and  electric  re- 
fining furnace  for  converting  this  into  steel  has  been  described 
by  Keller.* 

In  smelting  iron  ores  to  obtain  a  low  carbon  product,  the 
carbon  electrodes,  if  in  contact  with  the  slag  or  melting  ore,  will 
be  liable  to  more  rapid  corrosion  than  when  smelting  for  pig 
iron ;  on  account  of  the  scarcity  of  carbon  in  the  charge.  This 
difficulty,  if  it  were  found  to  be  serious,  might  be  overcome  by 
the  use  of  a  .furnace  like  that  of  De  Laval  (Fig  18,  p.  29),  in 
which  the  reduced  and  melted  metal,  collecting  in  two  troughs, 
serves  as  the  electrodes ;  electrical  contact  being  made  with  the 
molten  metal  by  solid  rods  of  the  same  material.  Another  plan 
for  avoiding  the  use  of  carbon  electrodes,  is  to  employ  the  induc- 
tion principle,  as  in  the  Snyder  Induction  furnace,  Fig.  47,  or 
in  some  Swedish  ore-smelting  furnacest  which  have  a  shaft  for 
the  reduction  of  the  ore,  while  the  molten  pig  iron,  resulting 
from  the  operation,  collects  in  an  annular  channel  where  it  is 
heated  by  an  induced  electric  current.  The  cost  of  producing 
low  carbon  steel  direct  from  pure  Italian  ore,  in  the  Stassano 
furnace,  has  been  estimated  by  Dr.  Goldschmidt,  who  sets  the 
cost  of  a  ton  of  such  steel  at  $18.80.  The  furnace  does  not 
utilize  the  heat  of  the  current  very  perfectly,  and  with  improved 
furnaces  and  better  conditions  for  the  purchase  of  general  sup- 
plies, a  lower  figure  might  be  expected. 

*Electrochemical   Industry,   vol..!.,   1903,   p.    162,  and  Journal   of   Iron  and   Steel   In- 
stitute,  1903,  No.    i,   p.   161. 

•f-Dr.    Haanel,    1907  Report,    p.    104. 


136  THE    ELECTRIC    FURNACE. 

CHAPTER    VI. 
Other  Uses  of  the  Electric  Furnace. 

The  production  of  iron  and  steel  in  the  electric  furnace  is  still 
in  its  infancy ;  and  will  be  limited  by  the  price  of  electrical  energy. 
But  there  are  many  other  uses  to  which  this  source  of  heat  has 
long  been  profitably  applied,  as  has  been  indicated  in  the  first 
two  chapters.  In  some  of  these  processes,  electrical  heat  is 
alone  <-  ble  to  produce  the  required  result,  while  in  others  the 
value  of  the  product  and  the  greater  economy  of  the  electrical 
method  has  enabled  it  to  supplant  the  older  processes,  even 
though  the  latter  employed  cheap  fuel  as  the  source  of  heat. 
Some  of  these  uses  of  the  electric  furnace  will  now  be  considered,, 
and  they  have  been  placed  for  convenience  under  the  following 
heads : — 

1.  The  Ferro-Alloys. 

2.  Graphite  and  the  Carbides. 

3.  Electrothermic  Production  of  Zinc. 

4.  Miscellaneous  uses  of  the  Electric  Furnace. 

5.  Electrolytic  Furnace  Operations. 

I.— The  Ferro=Al!oys. 

The  Ferro=Alloys. — The  alloys  of  iron  with  certain  metals> 
such  as  manganese,  chromium,  tungsten  and  titanium,  or  with 
the  metalloid  silicon,  are  often  known  as  the  ferros,  and  are 
usually  equivalent  to  cast  iron,  that  is  iron  with  a  large  percent- 
age of  carbon,  in  which  part  of  the  iron  has  been  replaced  by 
one  of  the  above  metals  or  metalloids.  In  some  cases,  how- 
ever, carbon  is  present  only  in  small  amounts  or  not  at  all,  and, 
on  the  other  hand,  more  than  one  of  the  alloying  metals  may 
be  present  in  the  same  ferro.  The  ferros  are  used  in  the  pro- 
duction of  steel  as  convenient  means  for  introducing  into  the 
steel  the  manganese  or  other  metal  which  they  contain ;  it  be- 
ing usually  less  costly  to  obtain  these  metals  as  ferro  alloys 
than  in  the  pure  state,  and  the  presence  of  the  iron  is  not  ob- 
jectionable in  additions  made  to  steel ;  although  the  carbon, 
which  is  also  usually  present,  is  sometimes  undesirable. 

The  metal  manganese  resembles  iron  in  many  particulars, 
but  is  more  difficult  to  reduce  from  its  ores,  and  when  this  is 
effected  in  the  blast  furnace,  with  iron  ore  to  furnish  enough 


FERRO    ALLOYS.  137 

iron  to  collect  and  alloy  with  the  manganese,  some  2*4  or  3 
tons  of  coke  are  required  to  produce  one  ton  of  the  80  per 
cent,  ferro-manganese,  and  about  20  per  cent,  of  the  manganese 
is  lost  in  the  slag  owing  to  the  imperfect  reduction  of  the  ore. 
Such  an  operation  is  very  wasteful,  both  in  fuel  and  in  the 
valuable  manganese  ore,  and  the  electric  furnace  is  so  much 
more  economical  in  both  these  particulars,  that  it  can  be  used 
in  competition  with  the  blast  furnace  method.  Silicon-eisen, 
that  is  low-grade  ferro-silicon  containing  some  10  or  15  per 
cent,  of  silicon,  can  be  made  in  the  blast  furnace  by  using 
silicious  charges  and  a  great  excess  of  fuel,  the  silicon  being  de- 
rived from  the  silica  in  the  charge.  In  the  electric  furnace, 
however,  using  quartz  as  the  source  of  silicon,  with  coke  to 
reduce  the  quartz  to  the  metallic  state,  and  some  iron  ore  or 
scrap  iron  to  alloy  with  the  silicon,  an  alloy  containing  as  much 
as  80  per  cent,  of  silicon  may  be  obtained ;  and  the  electric 
furnace  ferro-silicon  has  largely  displaced  the  blast  furnace  pro- 
duct, as  the  cost  of  the  former,  per  unit  of  silicon,  is  so  much 
less.  Some  other  ferro-alloys  are  also  made  more  cheaply  in 
the  electric  furnace. 

The  ferro-alloys  may  be  produced  in  electric  crucible 
furnaces,  such  as  the  Siemens  vertical  arc  furnace,  Fig.  2,  p.  4, 
or  the  Heroult  ore-smelting  furnace,  Fig.  29,  p.  108,  in  which 
a  carbon  electrode  dips  into  a  carbon-lined  receptacle,  which 
forms  the  other  electrode.  In  such  a  furnace  the  alloy  \vill 
usually  absorb  a  considerable  amount  of  carbon  from  the  lining, 
and  if  a  carbonless  alloy  is  required,  a  furnace  like  the  Heroult 
steel  furnace,  Fig.  23,  p.  87,  should  be  used,  in  which  two 
carbon  electrodes  are  employed,  which  need  not  touch  the 
molten  metal,  and  the  lining  of  the  furnace  is  not  made  of 
carbon. 

The  electro-metallurgy  of  silicon  is  described  by  Albert 
Keller,*  who  states  that  at  Livet,  with  4,000  H.P.,  he  was  able 
to  turn  out  20  tons  of -30  per  cent,  ferro-silicon  per  day,  and  that 
one  ton  of  the  alloy  requires  3,500  kilowatt  hours  for  its  produc- 
tion from  quartz,  scrap  iron  and  coke,  the  furnaces  being  each 
of  650  H.P. 

The  production  and  probable  uses  of  ferro-titanium  are  dis- 
cussed by  Auguste  J.  Rossi, t  who  reduces  tintaniferous  iron 
ores  in  the  electric  furnace,  either  with  carbon  or  with  the  as- 


*Keller,   Journ.    Iron   and   Steel   Inst.,   1903,  vol.   i.,   p.   iCf-. 

•f-Rossi,   Mineral  Industry,   vol.   ix.,    1903,  p.   715,   and   Trans.   Am.    Inst.   Min.   Engs., 
vol.    xxxiii.,    1903,   p.    191, 


138  THE     ELECTRIC     FURNACE. 

sistance  of  molten  aluminium,  which  serves  to  reduce  the  metal 
from  its  ore.  He  has  obtained  alloys  with  from  10  to  75  per 
cent,  of  titanium,  which,  when  aluminium  was  used  as  the  re- 
ducing reagent,  only  contained  a  few  tenths  of  one  per  cent,  of 
carbon.  Rossi  states  that  titanium  is  not  really  such  a  bugbear 
to  the  iron  metallurgist  as  is  usually  supposed,  but  that  on  the 
contrary  ferro-titanium,  added  to  either  pig  iron  or  steel, 
markedly  improves  the  mechanical  properties  of  the  metal.  In 
the  case  of  steel  he  suggests  that  the  w7ell-known  property  of 
titanium  of  combining  with  nitrogen  may  enable  it  to  remove 
this  gas  from  the  molten  metal,  and  in  this  way  to  improve  its 
quality.  A  company  has  recently  been  formed  to  manufacture 
ferro-titanium  in  the  electric  furnace,  and  is  building  a  plant  at 
Niagara  Falls.  * 

The  manufacture  of  ferro-nickel,  ferro-chrome  and  other 
alloys  of  iron  that  are  used  in  the  production  of  steel  are  de- 
scribed by  O.  J.  Steinhart.t  Ferro-chrome,  containing  from 
50  to  60  per  cent,  of  chromium,  was  made  at  one  time  by  heat- 
ing chromite  with  charcoal  in  crucibles,  and  later  in  small  blast 
furnaces,  but  is  now  made,  almost  entirely,  in  the  electric 
furnace.  The  Willson  Aluminium  Company  employed  4,000 
E.H.P.,  and  turned  out  200  to  250  tons  per  month  of  ferro- 
chrome  having  5  to  6  per  cent,  carbon  and  over  70  per  cent, 
chromium.  Their  works  at  Kanawha  Falls,  W.  Va.,  and  their 
business  and  patents  relating  to  the  manufacture  of  the  ferro- 
alloys have  been  acquired  by  the  Electrical  Metallurgical  Com- 
pany,! who  also  have  works  at  Niagara  Falls.  § 

The  Girod  Ferro-Alloy  Works  have  been  described  by  Dr. 
R.  S.  HuttonJI  who  draws  attention  to  the  wonderful  develop- 
ment of  the  hydro-electrical  installations  in  the  French  Alps 
and  the  application  of  this  power  to  electro-metallurgy.  The 
three  works  of  the  Societe  anonyme  Electrometallurgique.  Pn> 
cedes  Paul  Girod,  have  the  following  annual  output : — 

5,000  tons  of  50%  ferro-silicon. 

1,000  tons  of  30%  ferro-silicon. 

2,000  tons  of  ferro-chromium. 

800  to  900  tons  of  ferro-tungsten. 

About  50  tons  of  ferro-molybdenum. 

5  to  10  tons  of  ferro-vanadium. 

*£lectrochemical    Industry,    vol.    v.,    p.    69. 

fSteinhart,    Trans.    Inst.    Min.    and    Met.,   vol.    xv.,   1906,   p.    228. 

^Electrochemical    Industry,    vol.    v.,    p.    248. 

SElectrochemical    Industry,    vol.    v.,    p.    69. 

||R.    S.    Hutton,    Electrochemical    Industry,   vol.    v.,    p.    9. 


FERRO    ALLOYS.  139 

The  value  of  the  alloys  sold  is  more  than  $1,800,000  per 
annum.  Two  grades  of  ferro-tungsten  are  produced,  ''The  one 
containing  about  85%  tungsten,  and  a  maximum  of  0.5%  carbon, 
is  chiefly  employed  in  the  manufacture  of  crucible  tool  steels. 
The  other  quality  containing  6o%~7o%  tungsten,  and  2%-$% 
carbon  is  largely  used  for  the  manufacture  by  the  open-hearth 
process  of  steels  containing  less  than  2.5%  tungsten,  which  are 
used  for  the  manufacture  of  springs,  etc."  Analyses  of  typical 
products  of  these  works  are  contained  in  Table  XIV. 

TABLE  XIV. 

Analyses  of  Ferro-Alloys. 

Ferro-manganese     Spiegel-eisen  Silicon-Spiegel 
(blast  furnace),    (blast  furnace),   (blast  furnace). 

%o/  o/  o/  o/ 

/o  /o  /o  /o 

Manganese      82. oo2  8o.oo3  20.40*  15.003  19.003 

Iron       9.90  12.03  73-20  79-93  66.17 

Carbon      6.58  6.80  5-oo  4. 30            1.65 

Silicon        i.oo  0.90  i.io  0.50  13-00 

Sulphur       Trace  0.02  Trace  0.02            0.08 

Phosphorus       ....   0.12  0.25  0.06  0.25            o.io 

Arsenic        o.  10  o.  10 

Ferro-silicon, 
Blast-furnace.        Electric-furnace. 

%o/  o/  o/ 

/o  /o  /o 

Silicon        I4-853  78.80^  59.405  31.904 

Iron         82.95  12.64  36.85  61.30 

Manganese       °-34  °-3°          0.08  3.92 

Aluminium        4.76          2.73  0.22 

Calcium      2.32          o.  14  0.79 

Magnesium      0.22          0.17  0.26 

Carbon        1.66  0.55          0.218  0.50 

Sulphur       0.08                0.008  Trace  0.055 

Phosphorus      o.  12  0.051         0.056  0.027 

Chromium       o.  16  1.02 

Copper      0.04  o.oi 

Tungsten        o.oo  0.25 


2.  F.    \V.    Harbord,   The  Metallurgy   of   Steel,    p.   53 

3.  P.   Longmuir,   Elementary   Practical   Metallurgy,   Iron   and  Steel,   p     81. 

4.  G.  W.   Gray,  Journ.   Iron  and  Steel  Institute,  1901,  No.  a,  p.   144. 

5.  G.   W.    Gray,   Journ.    Iron   and   Steel   Institute,  1904,  No.    i,   p.   32. 


140 


THE    ELECTRIC     FURNACE. 

Ferro-chromium. 
Crucible  furnace.  Electric  furnace. 


Chromium     45-° 

Iron     45-° 

Carbon      8.6 

Silicon     0.6 

Manganese       ....    0.4 

Aluminium      o.o 

Magnesium       ....   o.o 

Sulphur       0.05 

Phosphorus       ....    0.05 


Ferro-tungsten, 
(Electric  furnace).1 

o/  o/ 

/o  /o 

Tungsten    ......  85.15     71-80 

Iron       .........  14.12     24.35 

Carbon        ......    °-45       2.58 

Silicon    ........    0.13       0.36 

Manganese      .  .  .    0.085 
Sulphur      ......    0.021 

Phosphorus      .  .  .    0.018 


6o.oo 

67.20 

64.17 

67.05 

65.90 

30.00 

3T-35 

32.47 

27.05 

23-44 

9.1 

0.90 

2-34 

4-25 

8.58 

0.5 

0.19 

0.38 

0.6O 

1.26 

0.3 

O.  12 

O.2I 

0.46 

0.44 

o.o 

O.OO 

0.13 

O.22 

O.l8 

o.o 

O.ig 

0.23 

0.3I 

0.14 

0.05 

O.006 

O.O23 

O.02 

0.02 

0.05 

O.O2I 

O.O2 

O.O2 

O.O2 

0.78 
0.02 
0.008 


Ferro-vanadium, 
(Electric  furnace). 


Vanadium    ....52.80 

Iron       ........  45-84 

Carbon      ......    1.04 

Silicon       ......    0.09 

Aluminium     ...    o.oo 
Sulphur    ......    °-Q2 

Phosphorus        .    0.02 


o/ 

/o 

34.10 

64.22 

1.42 

O.  12 
O.OO 
0.03 
O.OO9 


Ferro-molybdenum, 
(Electric  furnace).1 


Molybdenum        79-T5     83.80 


Iron       T7-52     12.72 

Carbon          3-24       3.27 

Sulphur         0.021     0.02 

Phosphorus        0.028     0.027 

In  dealing  with  these  and  other  products  of  the  electric 
furnace,  it  should  be  remembered  that  they  will  sometimes  evolve 
explosive  gases  if  allowed  to  come  in  contact  with  water.  This 
may  be  due  in  some  cases  to  small  quantities  of  calcium  carbide 
formed  at  the  high  temperature  of  the  electric  furnace,  but  in 
one  case,  that  of  some  ferro-silicon,  which  produced  a  number 


i.     R.    S.   Hutton,    Electrochemical   Industry,   vol.    v.,    p.    10. 


FERRO    ALLOYS.  141 

of  explosions  in  Liverpool  a  few  years  ago,*  the  explosive  gas 
was  found  to  be  phosphoretted  hydrogen.  The  alloy  was  very 
pure,  containing  nearly  60  per  cent  .of  silicon,  with  2.7  per  cent. 
of  aluminium,  0.2  per  cent,  of  carbon,  0.14  per  cent  of  calcium, 
0.17  per  cent,  of  magnesium,  and  0.56  per  cent  of  phos- 
phorus. 

Manganese,  nickel,  chromium,  tungsten  and  other  metals  can 
also  be  obtained  in  a  carbon-free  and  nearly  pure  state,  suitable 
for  use  in  the  manufacture  of  special  varieties  of  steel,  by  the 
Goldschmidt  process  of  mixing  the  oxide  of  the  metal  with 
powdered  aluminium  and  igniting  the  charge  by  means  of  a  small 
primer,  which  starts  the  reaction  between  the  oxide  and  the 
aluminium.  The  reaction  once  started  continues  throughout  the 
mass,  producing  an  intense  heat,  which  is  sufficient  to  melt  the 
reduced  metal  and  the  resulting  alumina. 

The  metalloid  silicon,  on  account  of  its  strong  affinity  for 
oxygen,  can  be  used  instead  of  aluminium  for  the  reduction  of 
such  metals  as  chromium,  tungsten  and  molybdenum  from  their 
oxides,  and  for  obtaining  alloys  of  these  metals  with  iron  01 
nickel.  Mr.  F.  M.  Beckett  has  patented  this  process,  and  de- 
scribes the  production  of  ferro-chrome,  low  in  carbon  and  silicon, 
by  feeding  a  mixture  of  chromite  and  metallic  silicon  into  an 
electric  furnace.  The  oxides  of  iron  and  chromium,  contained 
in  the  chromite,  are  reduced  to  the  metallic  state  by  reacting 
writh  the  silicon  according  to  the  following  equations  :  — 

20203  +  3Si  =  4Cr 


The  silica  resulting  from  the  reaction  is  slagged  off  by  the  basic 
impurities  present  in  the  chromite.  An  excess  of  the  chromite 
is  used  to  prevent  any  of  the  silicon  remaining  unoxidized  and 
alloying  with  the  ferro-chrome. 

Mr.  BecketJ  also  patents  the  use  of  silicon  or  ferro-silicon  for 
reducing  metals,  particularly  the  metals  molybdenum  and 
vanadium,  from  their  sulphide  ores.  The  following  equation 
shows  the  action  when  silicon  and  molybdenite  are  used  :  — 


*A.   Dupre  and  M.   B.  Lloyd,  Journ.   Iron  and  Steel  Inst.,  1904,  No.  i,  p.  30. 
fF.    M.    Becket,    U.S.    patent   854,018,    Electrochemical   Industry,   vol.   v.,   p.    237. 
+F.    M.   Becket,   U.S.    patent   855,157,   Electrochemical   Industry,   vol.   v.,  p.    237. 


142  THE    ELECTRIC    FURNACE. 

Mr.  E.  F.  Price*  has  also  secured  a  patent  for  the  production 
of  low-carbon  ferro-chromium,  etc.,  by  the  use  of  ferro-silicon. 
He  obtains  ferro-silicon  in  an  electric  furnace  and  then  taps  it 
into  a  second  electric  furnace,  where  it  is  made  to  re- 
act with  the  chromite,  for  the  production  of  ferro- 
chrome. 

II. — Graphite  and  the  Carbides. 

Graphite  : — The  elementary  substance  carbon  exists  in  nature 
in  three  distinct  forms  : — Amorphous  Carbon,  Graphite  and  the 
Diamond.  Amorphous  carbon  exists  in  a  nearly  pure  state  in 
such  substances  as  charcoal,  lampblack,  petroleum-coke,  and  the 
ordinary  electric  light  carbons.  Graphite  derives  its  name  from 
its  property  of  writing  on  paper,  and  is  largely  used  for  this 
purposes  in  the  common  "lead  pencil."  Plumbago  and  black- 
lead  are  other  names  for  graphite,  which  date  from  a  time  before 
the  true  nature  of  graphite  had  been  discovered,  and  when  it 
was  supposed  to  be  closely  related  to  lead  and  certain  of  its  ores.+ 
Natural  graphite  is  classified  as  crystalline  and  amorphous,  the 
former  occurs  in  flakes  or  flakey  masses  and  can  easily  be  freed 
from  associated  earthy  matter,  while  the  latter,  which  must  not 
be  confused  with  amorphous  carbon,  mentioned  above,  does  not 
occur  in  flakes,  and  is  therefore  not  so  easily  separated  from  the 
clayey  and  other  impurities  with  which  it  is  frequently  intimately 
associated,  t  Crystalline  graphite  is  largely  used  in  the  manu- 
facture of  pencils,  crucibles  and  lubricants,  while  the  less  valu- 
able amorphous  graphite  is  utilized  for  paints  and  foundry  facings. 
The  graphite  from  the  Borrowdale  mines  in  Cumberland,  although 
amorphous,  was  famous  for  many  years  as  the  best  for  making 
pencils ;  being  of  great  purity. 

The  diamond,  the  remaining  form  of  carbon,  is  remarkable 
for  its  great  hardness,  its  crystalline  form,  and  its  transparency 
when  pure.  It  has  been  produced  artificially  by  crystallization 
under  pressure  from  a  solution  of  carbon  in  molten  iron,  but  the 
process  has  not  attained  any  commercial  success.  § 

Graphite  differs  from  amorphous  carbon  in  the  following 
particulars  : — It  has  a  somewhat  higher  specific  gravity,  it  is  a 

*E.    F.    Price,    U.S.    patent,   852,347,    Electrochemical    Industry,    vol.    v.,    p.    278. 
•{•Graphite :    its    formation    and    manufacture,    by    E.    G.    Acheson,    Journ.    Franklin 
Institute,    1899. 

tGraphite,  by  E.   K.   Judd,  Mineral  Industry,  vol.  xiv.,  p.   309. 
^Artificial   diamonds,    Electrochemical   Industry,   vol.    iv.,    p.   343. 


GRAPHITE    AN7D    CARBIDES.  143 

better  electrical  conductor,  and  is  less  easily  oxidized  by  air  at  a 
red  heat  or  by  certain  chemical  reagents.  Its  greater  resistance 
to  oxidation  enables  it  to  be  used  in  the  manufacture  of  crucibles, 
and  this  and  its  good  electrical  conductivity  render  it  valuable  as 
a  material  for  electrodes  for  various  electro-chemical  and  electric- 
furnace  operations. 

It  has  been  known  for  a  long  time  that  amorphous  carbon 
and  the  diamond  could  be  converted  into  graphite  by  exposure  to 
very  high  temperatures  and  in  other  ways.  The  conversion  of 
amorphous  carbon  into  graphite  by  the  action  of  heat  is  only 
accomplished  at  the  highest  temperatures  of  the  electric  furnace, 
and  even  then  not  readily.*  When,  however,  some  metal  like 
iron  or  nickel,  which  has  the  property  of  dissolving  carbon  when 
in  the  molten  state,  is  saturated  with  that  substance,  and  then 
allowed  to  cool  slowly,  the  carbon  will  crystallize  or  separate 
from  the  cooling  metal  as  flakes  of  graphite.  The  separation  of 
graphite  from  molten  pig-iron  can  be  very  easily  noticed  in  a 
blast-furnace  casting  house.  The  method  by  which  large 
amounts  of  graphite  are  now  artificially  produced  depends  on  the 
formation  of  carbides  of  iron,  silicon,  etc.,  and  the  subsequent 
decomposition  of  these  carbides  at  a  still  higher  temperature,  the 
iron,  etc.,  being  driven  off  in  the  state  of  vapor,  leaving  the  car- 
bon in  the  form  of  graphite  and  of  a  high  degree  of 
purity. 

The  decomposition  of  carbide  of  silicon  yielding  graphite  in 
the  hottest  part  of  the  carborundum  furnace  had  been  noticed  by 
Mr.  Acheson  wrho  investigated  the  matter  and  found  that  pure 
forms  of  carbon  were  only  slightly  changed  into  graphite  in  the 
electric  furnace,  but  that  impure  carbon  such  as  ordinary  coke, 
or  carbon  to  which  certain  substances  such  as  iron  oxide,  silica, 
or  alumina  had  been  added,  were  largely  converted  into  graphite. 
Mr.  Acheson  patented  the  electric-furnace  production  of  graphite 
in  iSgGt  and  its  commercial  development  has  been  so  rapid 
that  in  1905  the  production  of  artificial  graphite  was  greater  than 
the  whole  output  of  natural  crystalline  graphite  in  the  United 
States. 


*F.  J.  FitzGerald.  The  conversion  of  amorphous  carbon  to  graphite,  Journ. 
Franklin  Institute,  1902. 

•f-E.  G.  Acheson,  U.S.  patent  568,323,  Sept.  29,  1896.  Converts  carbonaceous  ma- 
terials such  as  mineral  coal,  coke,  charcoal,  gas-carbon  and  carbides  into  practically 
pure  graphite,  by  employing  a  material  containing  a  considerable  proportion  of  mineral 
matter,  or  mixing  it  with  an  oxide  or  oxides,  such  as  silica,  clay,  alumina,  magnesia, 
lime  or  iron  oxide,  and  heating  the  mixture  in  an  electric  furnace,  Electrochemical 
Industry,  vol.  Hi.,  p.  482. 


'44  THE    ELECTRIC     FURNACE. 

The  electric-furnace  production  of  graphite*  is  illustrated  in 
Figs.  38  and  39.  The  former  showing  a  furnace  for  the  con- 
version of  anthracite  into  bulk  graphite,  while  the  latter 
illustrates  the  graphitization  of  electrodes  or  other  articles  of 
amorphous  carbon. 

Anthracite  has  been  selected  as  the  most  suitable  material 
for  the  production  of  graphite  in  bulk.  The  impurities  which 
are  disseminated  through  it  serving  as  carbide-forming  materials 
which  render  possible  its  conversion  into  graphite.  The  graphite 
furnace  consists,  as  is  shown  in  Fig.  38,  of  a  long  trough  which 
contains  the  anthracite,  and  of  two  electrodes  which  are  situated 
at  the  ends  of  the  furnace.  As  the  cold  anthracite  is  a  very  poor 
conductor  of  electricity,  a  core,  C,  of  carbon  rods  is  needed  to 
carry  the  current,  until  the  charge  becomes  heated.  The  furnace 
consists  of  a  permanent  base,  B,  and  end  walls,  AA,  which  sup- 
port the  electrodes.  The  side  walls,  DD,  are  not  permanent  but 
can  be  pulled  down  after  a  run.  The  base  of  the  furnace  is 
shown  supported  on  bricks  so  as  to  allow  of  air-cooling,  but  this 
precaution  is  not  always  taken.  The  electrodes  are  made  of  a 
number  of  graphite  rods,  E,  which  are  set  in  a  block  of  carbon 
as  shown  in  the  sketch  ;  electric  contact  being  made  by  a  terminal 
plate,  L,  which  may  be  water-cooled.  Above  the  charge  of 
anthracite,  H,  is  placed  a  cover,  K,  of  some  good  heat-insulating 
material,  which  should  also  be  a  very  poor  conductor  of  electricity. 

In  an  account  of  this  furnace  written  in  1902  by  Prof.  J.  W. 
Richards, t  it  is  said  to  be  30  feet  long  and  formed  of  a  trough 
2  feet  square,  lined  on  bottom  and  sides  with  blocks  of  compact 
carborundum  6  inches  thick.  Such  a  furnace  held  a  charge  of 
about  6  tons  of  anthracite  coal,  ground  to  the  size  of  rice,  and 
this  was  graphitized  in  twenty  hours.  The  author  is  informed  by 
the  Acheson  Graphite  Company  that  no  refractory  lining  is  now 
employed.  As  the  temperature  of  formation  of  graphite  in  this 
furnace  is  almost  certainly  over  2,ooo°C.,  it  must  be  well  above 
the  melting  point  of  ordinary  fire-clay  bricks,  and  a  furnace  such 


*E.  G.  Acheson,  U.S.  patent  645,285,  March  13,  1000,  Producing  graphite  by  heat- 
ing anthracite,  etc.,  Electrochemical  Industry,  vol.  iv.,  p.  42. 

Manufacturing  graphite,  British  patent  2,116,  of  1901,  by  O.  Imray,  of  the  Inter- 
national Acheson  Graphite  Company,  Electrochemist  and  Metallurgist,  vol.  i.,  p.  131. 

Manufacturing  of  artificial  graphite  from  charcoal,  J.  Weckbecker,  illustrated  ac- 
count, Electrochemical  Industry,  vol.  ii.,  p.  244. 

Process  of  Making  Graphite,  E.  G.  Acheson,  U.S.  Patent,  711,031,  Electrochemical 
Industry,  vol.  i.,  p.  130. 

fThe  Electrochemical  Industries  of  Niagara  Falls,  J.  W.  Richards,  Electrochem. 
Industry,  vol.  i.,  p.  52. 


GRAPHITE    AND    CARBIDES. 


Ui 


146  THE     ELECTRIC     FURNACE. 

as  is  shown  in  Fig.  38  could  only  be  operated  if  the  bottom  and 
walls  were  composed  of  or  lined  with  some  specially  refractory 
material,  or  if  it  were  possible  to  leave  a  layer  of  unconverted 
anthracite  between  the  furnace  walls  and  the  remainder  of  the 
charge. 

By  increasing  the  cross  section  of  the  charge  there  would  be 
less  danger  of  the  walls  becoming  overheated  and  the  graphitiza- 
tion  of  the  central  portion  of  the  anthracite  might  still  be  effected 
provided  the  electric  current  could  be  concentrated  on  this  por- 
tion instead  of  spreading  over  the  whole  of  the  cross  section.  At 
the  beginning  of  the  run  the  current  will  pass  almost  entirely 
through  the  core  of  carbon  rods,  and  when  this  conducting  core 
is  augmented  by  the  conversion  of  the  surrounding  anthracite  into 
graphite,  its  electrical  resistance  will  become  so  low  that  there 
will  be  little  tendency  for  the  current  to  pass  through  the  outer 
portions  of  the  charge.* 

The  electrode  furnace, t  Fig.  39,  resembles  the  graphite 
furnace  in  construction.  The  electrodes  or  other  articles  to  be 
graphitized  are  placed  in  piles  with  their  length  across  the  length 
of  the  furnace,  in  order  to  keep  the  electrical  resistance  as  high 
as  possible.  They  are  surrounded  by  broken  coke,  which  has 
u  moderately  high  resistance,  so  that  most  of  the  heat  is  de- 
veloped in  the  parting  layers  of  coke,  and  the  current  will  tend 
to  pass  through  the  electrodes  in  the  middle  of  the  furnace,  rather 
than  through  the  outer  parts  of  the  furnace  which  are  filled  with 
the  broken  coke.  The  coke  will  consequently  serve  as  a  jacket 
to  retain  the  heat  and  prevent  the  overheating  of  the  walls  of  the 
furnace.  The  dimensions  of  the  furnace  depend  upon  the  size 
of  the  electrodes,  which  can  be  as  much  as  4  feet  in  length.  A 
cover  of  some  heat-insulating  substance  is  employed,  but  there  is 
no  refractory  lining  of  carborundum,  etc.,  such  as  was  described 
in  the  patents  and  earlier  accounts. 

In  the  plant  of  the  International  Acheson  Graphite  Com- 
pany at  Niagara  Falls  there  are  6  furnaces  of  750  or  800  K.W., 
and  10  furnaces  of  1,600  K.W.  The  total  power  employed  is 


""Compare  the  account  of  the  manufacture  of  soft  graphite,  where  an  outer 
portion  or  jacket  of  poorly  conducting  material  is  provided. 

•f-Graphitizing  electrodes  and  other  carbonaceous  articles.  Patent  application, 
November  2yd,  1900,  with  illustration  of  electrode  furnace.  Electrochemist  and 
Metallurgist,  vol.  i.,  1901,  p.  54. 

The  Ruthenburg  and  Acheson  Furnaces,  F.  A.  J.  FitzGerald,  Electrochemical  In- 
dustry, vol.  iii.,  p.  417. 

E.  G.  Acheson  U.S.  patent  617,979,  January  i7th,  1899,  and  702,758;  June  i7th, 
1902,  Graphite  electrodes,  etc.  Mentions  current  and  size  of  furnace,  Electrochemical 
Industry,  vol.  iv.,  p.  42. 


GRAPHITE    AND    CARBIDES.  147 

2,400  K.W.,  operating  one  furnace  of  each  size;  the  other 
furnaces  being  in  process  of  cooling,  emptying  or  recharging. 
Each  furnace  takes  about  half  a  day  to  heat,  and  four  or  five 
days  to  cool.  The  total  output  of  the  plant  in  1906  being  nearly 
6,000,000  Ibs.  of  graphite.  The  electrical  current  is  supplied  at  a 
voltage  of  2,200.  This  is  transformed  to  a  current  at  200  volts, 
and  the  voltage  is  further  lowered  by  a  special  regulator  as  the 
resistance  of  the  charge  decreases  during  the  run,  so  that  all  the 
available  power  can  be  applied  during  the  whole  period.  J.  W. 
Richards  states  that  for  the  electrode  furnaces  the  current  is  3,000 
amperes  at  220  volts  to  begin  with,  and  9,000  amperes  at  80 
volts  at  the  end  of  the  operation.  The  current  flowing  through 
the  i, 600  K.W.  furnaces  must  be  about  twice  as  large  as  this. 

The  conversion  of  amorphous  carbon  into  graphite  in  the 
Acheson  furnace  is  supposed  to  be  due  to  the  formation  and 
subsequent  decomposition  of  carbides  of  the  iron  and  other 
metals  contained  in  the  charge.  It  should  be  noted,  however, 
that  the  amount  of  iron,  aluminium,  calcium,  etc.,  contained  in 
the  anthracite,  or  specially  added  to  the  electrodes,  is  not  nearly 
enough  to  combine  with  all  the  carbon  to  form  carbides,  as  the 
ash  or  impurity  in  anthracite  varies  from  about  5%  to  about  15%, 
and  the  amount  of  iron  ore,  etc.,  which  is  added  to  the  electrode 
material  in  order  to  enable  the  manufactured  electrode  to  be 
graphitized  is  only  2%  or  3%.  These  metals  may  be  expected  to 
serve  for  more  than  one  equivalent  of  carbon,  because  when  the 
central  part  of  the  furnace  has  become  hot  enough  to  dissociate 
the  carbides  that  had  formed  there,  the  volatilized  metals  will 
escape  to  cooler  zones,  and  will  again  form  carbides  with  the 
carbon  at  that  point ;  but  this  explanation  hardly  accounts  for 
all  the  carbon  that  is  graphitized  through  the  agency  of  a  very 
small  amount  of  added  metal,  although  it  undoubtedly  explains 
in  part  the  great  effect  of  these  added  bodies.  Another  factor 
will  be  found  in  the  consideration  that  dissociation  and  reforma- 
tion of  the  carbides  is  always  taking  place  at  temperatures  below 
that  of  the  final  splitting  up  of  these  bodies,  and  that  in  this  way 
the  small  amount  of  metal  can  eventually  form  carbides  with  all 
the  carbon  in  the  furnace.  From  this  point  of  view,  time  would 
appear  to  be  an  essential  element  in  the  conversion  of  carbon 
into  graphite,  and  this  is  probably  the  case,  although  at  the  high 
temperature  of  the  graphite  furnace  these  molecular  combinations 
and  dissociations  will,  no  doubt,  take  place  with  great  rapidity. 

The  character  and  uses  of  Acheson  graphite  are  fully  de- 
scribed in  a  series  of  pamphlets  issued  by  the  International 


148  THE    ELECTRIC     FURNACE. 

Acheson  Graphite  Company,*  and  in  other  published  papers, t 
from  which  the  following  points  may  be  summarized.  The  real 
density  of  natural  graphite,  and  of  the  Acheson  graphite 
electrodes  is  2.25,  while  the  real  density  of  amorphous  carbon 
varies  from  1.5  to  1.9.  The  graphite  electrodes  are  very  pure 
containing  certainly  less  than  i%,  and  often  only  o.  i%  of  im- 
purity, t  The  electrical  conductivity  of  the  graphite  electrodes 
is  about  four  times  that  of  amorphous  carbon  electrodes,  and  the 
cross  section  of  an  electrode  can  be  proportionately  decreased 
when  the  graphite  variety  is  employed.  Graphite  electrodes  are 
found  to  have  a  far  longer  life  than  those  of  amorphous  carbon 
when  used  in  a  variety  of  electrolytic  processes  ;  the  rate  of  cor- 
rosion and  disintegration  being  very  much  less.§  The  graphite 
electrodes  have  another  valuable  property,  namely,  that  of  easy 
cutting  or  machining.  II  Electrodes  of  amorphous  carbon  are  very 
difficult  to  cut,  and  must  usually  be  moulded  into  any  required 
shape,  while  the  Acheson  graphite  electrodes  can  be  cut  with  a 
saw,  drilled,  threaded,  etc.,  so  that  all  kinds  of  shapes  can 
readily  be  prepared  from  rods  or  slabs  of  the  graphite.  In 
particular,  it  is  possible  to  avoid  wasting  the  ends  of  electrodes, 
by  the  use  of  threaded  connections,  as  in  Fig.  32,  so  that  when 
an  electrode  becomes  too  short  for  further  use,  another  is  attach- 
ed to  its  outer  end,  and  the  lengthened  electrode  can  be  fed 
steadily  forward  into  the  furnace  or  electrolytic  tank  without  in- 
terruption of  the  process  or  waste  of  electrode.  In  electrolytic 
work,  composite  electrodes  are  often  used ;  a  slab  of  graphite 
serves  as  the  working  electrode,  being  immersed  in  the  elctrolyte, 
and  one  or  more  graphite  rods  which  are  threaded  into  the  slab, 
serve  to  support  it  and  lead  in  the  electrode  current. 


*Acheson  Graphite  Electrodes.  Pamphlet  by  The  International  Acheson  Graphite 
Company. 

•f-Graphite  Electrodes  in  Electrometallurgical  Processes.  C.  L.  Collins,  Amer. 
Electrochem.  Soc.,  vol.  i.,  p.  53. 

•Uses  of  Acheson  Graphite  in  Metallurgical  Research,  W.  McA.  Johnson,  Electro- 
chemical Industry,  vol.  ii.,  p.  345. 

Graphite  electrodes  for  electric  furnace  work,  Electrochemical  Industry,  vol.  iv., 
p.  513.  The  Acheson  Graphite  Company  supplied  2,404,171  pounds  of  graphitized 
electrodes  during  the  year  ending  July  ist,  1906. 

+The  pamphlet  on  Acheson  Graphite  Electrodes,  dated  1902,  states  that  the 
percentage  of  impurities  averages  about  i  part  in  1,000,  and  quotes  an  experiment  in 
which  their  electrodes  yielded  0.8  per  cent,  of  ash.  A  later  leaflet  on  Acheson 
Graphite  states  that  the  electrodes  contain  99.5  per  cent,  of  pure  graphitic  carbon. 

gGraphite  Electrodes  in  Electrolytic  Work,  by  C.  L.  Collins,  Electrochemical  In- 
dustry, vol.  i.,  p.  26. 

[[Adaptability  of  Acheson  Graphite  Articles,  or  Ease  of  Machining.  Acheson 
Graphite  Company,  1904,  and  paper  by  C.  L.  Collins,  Electrochemical  Industry,  vol.  ii., 
p.  277. 


GRAPHITE    AND    CARBIDES.  149 

Mr.  Acheson  has  recently  succeeded  in  producing  a  specially 
soft  variety  of  graphite  which  is  found  to  be  a  very  efficient 
lubricant.* 

It  is  made  in  the  electric  furnace  from  anthracite  or  other 
form  of  amorphous  carbon  to  which  a  larger  amount  than  usual  of 
carbide  forming  material  has  been  added.  Silica  is  preferred  as 
an  addition,  because  it  does  not  form  a  fusible  carbide.  The 
amount  added  being  far  greater  than  is  added  in  the  manu- 
facture of  graphite  electrodes,  or  is  present  in  the  conversion  of 
anthracite  into  bulk  graphite,  but  it  is  less  than  would  be  re- 
quired for  making  a  carbide  with  the  whole  of  the  carbon.  The 
following  specific  case  is  contained  in  the  patent  application  :t — 

"An  electric  furnace,  having  a  length  of  18  feet  between  terminal 
electrodes,  was  provided  with  a  starting  core  consisting  of  a  graphite 
rod  ^-inch  in  diameter.  The  active  zone,  18  inches  in  diameter,  sur- 
rounding this  core  was  filled  with  a  mixture  of  carbonaceous  material 
and  carbide-forming  oxide.  The  materials  used  in  this  specific  in- 
stance were  anthracite  coal,  ground  to  pass  through  a  ^-inch  mesh, 
mixed  with  sand,  in  the  proportion  of  65  per  cent,  coal  and  35  per  cent, 
sand,  the  ash  contained  in  the  coal  being  calculated  as  a  part  of  the 
sand  content  of  the  mixture.  Completely  surrounding  the  active  zone 
above  referred  to  was  disposed  a  mixture  of  anthracite  coal  and  sand  in 
the  proportion  of  i  part  coal  to  2  parts  of  sand,  this  mixture  having  a 
much  higher  resistance  than  that  in  the  active  zone,  and  serving  as  an 
effective  heat  retainer.  The  furnace  being  charged  in  this  manner  the 
electric  current  was  turned  on,  and  at  the  beginning  registered  79 
volts  and  75  kilowatts.  After  2  hours,  the  register  showed  203  volts 
and  200  kilowatts,  and  after  9^  hours  showed  135  volts  and  800  kilo- 
watts. The  register  at  the  end  of  15  hours  still  showed  800  kilo- 
watts, while  the  volts  had  dropped ^to  70,  as  the  result  of  decreased 
internal  resistance,  due  to  the  formation  of  graphite.  When  cold  the 
furnace  was  opened  and  962  pounds  of  soft,  unctuous  and  non- 
coalescing  graphite  \vere  removed  from  the  active  zone." 

Kryptol,t  a  specially  prepared  material  for  use  as  a  resistor 
in  electric  heaters  and  furnaces,  appears  to  consist  of  a  mixture 
of  graphite  and  amorphous  carbon,  in  grains  of  nearly  uniform 
size.  This  material  can  be  given  a  higher  or  lower  electrical 
conductivity  by  varying  the  proportion  of  graphite  and  amorphous 
carbon,  and  by  changing  the  size  of  the  grains  of  which  the  ma- 
terial is  formed. 

Carborundum.  The  discovery  of  this  carbide  by  E.  G. 
Acheson  in  i8gi,§  was  the  first  step  leading  to  the  considerable 
industries  at  Niagara  Falls,  with  which  he  is  nowr  associated. 


*Soft  Graphite,   Electrochemical   Industry,  vol.   iv.,  pp.   343,   and  502. 

fSoft  Graphite.  E.  G.  Acheson,  U.S.  Patent  836,355,  Electrochemical  Industry, 
vol.  iv.,  p.  502. 

+Kryptol,  Electrochemical  Industry,  vol.  ii.,  pp.  333,  and  463,  vol.  iii.,  pp.  5,  127, 
and  157,  and  vol.  iv.,  pp.  148,  210,  250,  296,  and  344. 

§See   page   10. 

II 


I5O  THE    ELECTRIC    FURNACE. 

The  metal  silicon  is  perhaps  the  most  abundant  metal  in  the 
world,  forming  nearly  50%  of  the  widely  spread  substance  silica, 
which  is  the  oxide  of  silicon.  Its  affinity  for  oxygen  is  so  great, 
however,  that  until  the  advent  of  the  electric  furnace  it  could  only 
be  isolated  with  the  greatest  difficulty.  In  the  higher  ranges  of 
temperature  afforded  by  the  electric  current,  the  metal  is  not  only 
readily  reduced  from  its  oxide  by  means  of  carbon,  but  the  re- 
duced metal  combines  with  carbon  to  form  a  carbide  having  the 
formula  SiC.  This  carbide  is  amorphous  when  it  is  first  formed, 
but  on  being  more  strongly  heated  it  crystallizes  and  is  then 
known  as  carborundum.  The  formation  of  the  carbide  may  be 
represented  by  the  following  equation  :  — 


Carborundum  is  produced  by  heating  a  mixture  of  coke, 
silicious  sand,  sawdust  and  salt  in  an  electric  furnace  such  as  is 
shown  in  operation  in  Fig.  40,  and  diagramatically  in  Fig.  8, 
p.  ii.  The  charge  is  made  approximately  in  the  following  pro- 
portions: —  Coke,  34.2%;  sand,  54.2%;  sawdust,  9.9%;  and  salt, 
1.7%;  the  sand  and  the  carbon  in  the  coke  and  sawdust  being 
nearly  in  the  proportion  indicated  by  the  equation.  The  saw- 
dust contained  in  the  charge  has  the  effect  of  rendering  it  more 
porous  and  of  allowing  the  gases  to  escape  more  freely,  while 
the  salt  is  found  to  facilitate  the  running  of  the  furnace. 

Later  accounts  show  a  larger  proportion  of  salt  and  a  smaller 
amount  of  sawdust  in  the  charge.  J.  W.  Richards,*  writing  in 
1902,  and  describing  a  furnace  of  750  K.W.,  says,  "The  total 
contents  of  the  furnace  are  about  1,000  pounds  of  carbon  core, 
and  the  mixture  reduced  represents  3.5  tons  of  carbon  mixed 
with  6  tons  of  silica  sand  and  1.5  tons  of  salt,  producing  in  a 
thirty-six-hour  run  between  3  and  4  tons  of  commercial 
carborundum,  in  crystals,  outside  of  which  is  a  quantity  of  light- 
green  amorphous  carborundum,  fully  reduced,  but  uncrystallized, 
and  outside  of  this  the  unchanged  mixture."  E.  G.  Acheson's 
United  States  patent  No.  560,291,  May  igth,  1896^  for  a  car- 
borundum furnace  of  1,000  K.W.  specifies  a  mixture  of 
"20  parts  (by  weight)  of  finely  divided  coal  or  coke, 
29  parts  of  sand,  5  parts  of  common  salt,  and  2  parts  of  saw- 
dust." 


"The     Electrochemical     Industries     of     Niagara    Falls,     J.     W.    Richards,    Electro- 
chemical   Industry,   vol.    i.,    p.    50. 

•J-E.    G.    Acheson,    U.S.    patent    560,291,    Electrochemical    Industry,    vol.    v.,    p.     7j> 
An   earlier   patent,   492,767,   February   28th,   1893,   is   abstracted  in  vol.   v.,   p.   36. 


GRAPHITE  AND  CARBIDES.  151 

The  mixture  of  coke,  sand,  etc.,  is  not  a  good  conductor  of 
electricity,  and  the  heating  must  therefore  be  effected  by  means 
of  a  core  of  broken  coke,  marked  E  in  Fig.  8,  which  extends 
between  the  two  electrodes,  C  and  D,  and  serves  as  a  resistor, 
carrying  the  electric  current  and  heating  the  surrounding  charge. 


.    •  -  - 

Fig.  40. — Carborundum  Furnace  Burning. 

The  coke  for  making  up  the  charge  is  ground  to  a  powder,  but 
the  coke  for  the  resisting  core  is  in  small  pieces  about  %  or  ^ 
inch  in  size,  from  which  the  dust  has  been  removed.  The  core  is 
circular  in  section  and  is  built  up  by  hand  after  the  furnace  has 
been  half  filled,  a  packing  of  fine  carbon  powder  serves  to  make 
good  electrical  contact  between  the  core  and  the  carbon  electrodes. 


152  THE     ELECTRIC     FURNACE. 

The  electrodes  consist  of  a  number  of  square  rods  of  carbon  or 
graphite,  which  are  held  by  heavy  bronze  holders  F  and  G. 
Electrical  contact  with  the  carbon  rods  being  rendered  more 
perfect  by  means  of  a  series  of  copper  strips,  indicated  by  black 
lines  in  Fig.  8,  which  are  laid  between  the  rows  of  carbon  rods 
and  are  connected  to  the  bronze  holders  or  directly  to  the  cables 
from  the  bus  bars.  The  general  construction  of  the  furnace  is 
similar  to  that  of  the  graphite  furnaces,  the  end  walls  and  bottom 
of  the  furnace  being  permanent,  while  the  side  walls  are  loosely 
built,  allowing  the  carbonacous  gases  to  escape  and  burn  as  shown 
in  Fig.  40,  and  are  taken  down  between  the  operations  to  allow  of 
emptying  and  refilling  the  furnace.  The  electrical  equipment  is 
similar  to  that  of  the  graphite  furnaces,  but  there  are  more 
electrical  units  provided,  as  3,  750  K.W.  furnaces  and  i,  1,000 
K.W.  furnace  can  be  operated  at  once. 

The  Carborundum  furnace  has  been  described  by  F.  A.  J. 
FitzGerald*  who  gives  a  scale  drawing  of  a  750  K.W.  furnace. 
The  furnace  was  i6j4  feet  long,  6  feet  wide,  and  5  T-2  feet  high 
inside,  and  has  a  core  of  coke,  16  feet  long  and  20  inches  in 
diameter.  In  the  patent  just  referred  to  a  furnace  of  1,000  K.W. 
was  stated  to  have  a  core  8  feet  long  and  10  inches  in  diameter, 
composed  of  grains  3/16  of  an  inch  in  diameter,  of  coked 
bituminous  coal. 

At  the  end  of  the  operation  the  carborundum  is  found  in  a 
cylindrical  crystallized  mass  surrounding  the  core,  and  around 
the  carborundum  is  a  layer  of  uncrystallized  carbide  which  has 
been  called  carborundum  fire-sand.  In  the  furnace  figured  by 
FitzGerald  the  carborundum  cylinder  is  50  inches  in  diameter.  The 
layer  of  fire-sand  is  often  i  inch  or  i  ^  inches  in  thickness.  The 
grains  of  coke  composing  the  core  have  become  partly  graphitized. 
They  can  be  used  again,,  and  their  use  will  be  better  in  general 
than  that  of  fresh  coke  as  the  resistance  of  the  core  will  be  less 
variable  when  they  are  used.  The  temperature  of  the  furnace  is 
highest  in  the  middle,  that  is  just  around  the  core,  and  the  inner 
part  of  the  carborundum  may  be  heated  above  its  dissociation 
temperature  and  be  converted  into  graphite,  the  silicon  being 
volatilized  and  driven  into  the  cooler  parts  of  the  furnace.  The 
accidental  formation  of  graphite  in  this  way  led  to  its  regular 
manufacture  in  the  Acheson  furnace.  The  temperature  of  the 
carborundum  furnace  has  never  been  measured  and  has  been  sup- 
posed to  be  as  high  as  3,ooo°C.  Measurements  by  Messrs. 


*The  Carborundum   Furnace,  F.   A.  J.   FitzGerald,  Electrochemical  Industry,  vol.  iy., 
P-    53- 


GRAPHITE    AND    CARBIDES.  153 

Tucker   and    Lampen   put   the  dissociation    temperature   of    car- 
borundum,   and     therefore   the    hottest     part   of    the    furnace  as 

2,220°C. 

The  consumption  of  energy  per  pound  of  carborundum  was 
given  by  J.  \Y.  Richards  as  3.8  K.W.  hours.  The  output  in 
1905  was  5,596,000  Ibs.  Its  main  use  is  as  an  abrasive,  being 
used  instead  of  emery,  it  is  made  into  wheels,  sticks,  hones,  etc., 
the  masses  of  carborundum  being  crushed,  washed  and  graded 
into  powders  of  varying  degrees  of  fineness.  These  powders  are 
usually  cemented  together  to  form  the  carborundum  articles  by 
moulding  with  kaolin  and  feldspar  and  firing  in  a  kiln,  but  a 
method  has  been  devised*  for  making  solid  blocks  of  carborundum 
by  cementing  the  grains  together  with  thin  glue,  and  then  heating 
in  the  electric  furnace  to  the  temperature  of  the  formation  of 
carborundum.  The  grains  become  firmly  cemented  together. 
The  uses  of  carborundum  and  carborundum  fire-sand  as  refractory 
materials  have  been  referred  to  in  Chapter  IV.  The  Carborundum 
Company  are  nowr  erecting  a  plant  at  Duesseldorf  in  Germany  for 
the  manufacture  of  carborundum  for  the  European  market. t 

Siloxicon.  This  term  covers  a  series  of  compounds  of  silicon, 
carbon  and  oxygen,  having  the  general  formula  SixCxO,  which 
are  produced  in  the  electric  furnace  by  heating  a  mixture  of  car- 
bon and  silica,  in  which  there  is  not  enough  carbon  to  form  car- 
bide of  silicon  with  the  whole  of  the  silica.  This  material  was 
patented  by  Mr.  Acheson  in  1902.^  The  proportions  indicated 
in  the  patent  are  one  part  of  powdered  carbon  to  two  parts  of 
powdered  silica.  The  mixture  must  not  be  heated  to  the  tempera- 
ture of  the  formation  of  carborundum,  because  at  that  temperature 
silixicon  dissociates  into  carborundum,  silicon  and  carbon  mon- 
oxide. On  account  of  the  danger  of  overheating,  it  is  desirable 
to  employ  a  furnace  with  a  number  of  cores,  moderately  heated  ; 
this  arrangement  enabling  a  large  volume  of  the  charge  to  be 
heated  to  a  nearly  uniform  temperature,  and  thus  giving  a  better 
yield  of  the  siloxicon.  Such  a  furnace  is  shown  diagramatically 
in  Fig.  41,  the  core  consisting  of  a  large  number  of  rods  of 
graphitized  carbon  connected  together  by  being  fitted  into  blocks 
of  graphite.  In  the  furnace  shown  the  rods  are  arranged  partly 
in  series  and  partly  in  parallel,  y$  of  the  entire  current  passing 
through  each  rod.  The  graphite  blocks  are  shown  supported  on 


*F.   A.    J.    FitzGerald,  U.S.   patent  651,2^4,  Electrochemical   Industry,   vol.   v.,  p.   70. 
•f-Electrochemical    Industry,    vol.    iv.f    p.    348. 

^Refractory    Material,     E.    G.    Ache- n,    V.S.    patent    722,79?.       Electrochemical    In- 
dustry, vol.  i.,  p.    287. 


*54 


THE     ELECTRIC     FURNACE. 


a  layer  of  some  refractory  material  on  the  bottom  of  the  furnace. 
Siloxicon,  the  most  usual  formula  for  which  is  Si2C2O,  is  a  loose 
powdery  gray-green  amorphous  material,  and  can  readily  be  re- 
moved from  the  furnace  after  taking  down  the  side  walls,  by  rak- 
ing it  out  from  between  the  cores.  Such  a  furnace  might  be  em- 
ployed for  the  manufacture  of  amorphous  silicon  carbide,  but 
could  not  be  used  for  the  production  of  the  crystallized  carborun- 
dum, as  the  system  of  cores  would  be  destroyed  after  each  opera- 


Fig.  41. — Multiple  Core  Furnace. 

tion.        Siloxicon   forms    a  valuable   refractory    material,    and  its 
properties  and  uses  have  been  described  in  Chapter  IV. 

Calcium  Carbide.  This  carbide  is  universally  known  on  ac- 
count of  the  ease  with  which  it  reacts  with  water,  liberating  the 
valuable  illuminant  acetylene.  The  possibilities  suggested  by  the 
discovery  of  this  portable  gas-producing-  substance  naturally  led 
to  a  very  rapid  development  of  its  manufacture.  Very  many  dif- 
ferent forms  of  electric  furnaces  have  been  devised  for  its  produc- 
tion, and  whole  books  have  been  devoted  to  a  description  of  its 
manufacture  and  uses. 


GRAPHITE    AND    CARBIDES.  155 

The  carbide  is  produced  by  heating  lime  and  coke  or 
anthracite  in  an  electric  furnace  to  a  temperature  which  has  been 
stated  by  Moissan  to  be  3,ooo°C.  The  lime  and  carbon  react 
forming  the  carbide  which  is  fluid  at  this  temperature,  and  may 
be  tapped  from  the  furnace  or  allowed  to  solidify  into  a  block 
and  broken  up  when  cool.  The  following  reaction  takes  place  :  — 


When  the  carbide  comes  in  contact  with  water,  acetylene  is  formed 
as  follows  :  — 

CaC2  +  2H2O  =  Ca(OH)2  +  C2H2. 

Calcium  carbide  has  usually  been  made  in  arc  furnaces,  such  as 
the  Willson  furnace,  Fig.  7,  p.  10,  but  recently  resistance  furnaces 
have  been  employed,*  furnaces  of  500  horse-power  and  1,200 
horse-power  having  been  installed  in  French  plants.  The  voltage 
of  these  resistance  furnaces  is  only  about  30  or  40  volts  instead  of 
bo  which  was  the  usual  figure  with  arc  furnaces. 

The  inventor,  T.  L.  Willson,  in  his  patents  gives  35%  of  coke 
and  65%  of  quicklime  as  the  best  proportions  for  the  mixture, 
and  states  that  i  pound  of  the  carbide  will  yield  about  5^  cubic 
feet  of  acetylene. 

Digests  of  a  number  of  calcium  carbide  patents  will  be  found 
in  volume  v.  ,  of  the  Electrochemical  Industry.  A  large  number 
of  electric  furnaces  for  the  production  of  calcium  carbide  are  de- 
scribed and  figured  in  V.  B.  Lewes'  Acetylene,  and  Borchers' 
and  other  books  on  electric  smelting. 

III.  —  Electrothermic  Production  of  Zinc. 

Although  zinc  is  one  of  the  common  metals,  and  has  long 
been  produced  in  furnaces  fired  by  coal  or  gas,  its  volatility  and 
the  ease  with  which  it  becomes  oxidized  present  serious  difficulties 
in  the  treatment  of  its  ores,  and  many  attempts  have  been  made 
to  overcome  these  difficulties  by  smelting  ores  of  zinc  in  the 
electric  furnace. 

In  the  usual  process  of  zinc  smelting,  the  ores  are  first  roasted 
to  remove  the  sulphur  in  the  case  of  sulphide  ores,  or  the  carbonic 
acid  in  the  case  of  carbonate  ores,  and  the  resulting  oxide  of  zinc 
is  mixed  with  about  one-half  its  weight  of  coal  and  heated  in  re- 
torts or  muffles  made  of  fire-clay.  In  order  to  complete  the  re- 
duction of  the  oxide  to  the  metallic  state  it  must  be  heated  to  a 


'Electrochemical    Industry,    vol.    iv.,    p.    27. 


156  THE  ELECTRIC  FURNACE. 

temperature  above  the  boiling  point  of  the  zinc,  which  is  conse- 
quently given  off  as  vapor,  passing  in  that  form  out  of  the  retort, 
and  is  condensed  to  the  liquid  metal  in  a  condenser,  from  which 
ii  can  be  removed  and  poured  into  moulds. 

The  residue  is  then  removed  from  the  retort  and  the  opera- 
tion repeated.  The  retorts  are  heated  externally  by  coal  or  gas 
firing,  and  as  the  ore  must  be  heated  to  about  i,2oo°C.,  or 
2,20o°F.,  the  retorts  cannot  usually  be  made  very  large,  and 
frequently  only  hold  about  100  pounds  of  the  ore  mixture,  from 
which  it  will  be  seen  that  the  cost  of  labor  in  zinc  smelting  is 
likely  to  be  high.  The  utilization  of  heat  in  these  furnaces  is  also 
very  poor  on  account  of  its  slow  transmission  through  the  walls 
of  the  retorts,  the  heat  efficiency  of  such  a  furnace  being  given 
by  Prof  .Richards*  as  under  7  per  cent.  At  the  high  temperature 
of  zinc  distillation  the  retorts  only  last  about  a  month,  and  their 
renewal  forms  a  considerable  item  of  expense.  Other  difficulties 
are  met  in  the  condensation  of  the  zinc  vapor,  as  this  does  not  all 
collect  in  the  liquid  state,  but  in  part  as  a  powder,  which  cannot 
be  melted  together,  while  a  part  of  the  vapor  escapes  altogether. 

Most  of  the  difficulties  that  have  been  referred  to  are  caused 
by  the  necessity  of  heating  the  ore  in  a  number  of  small  retorts, 
heated  externally,  instead  of  in  a  large  furnace  in  which  the  heat 
could  be  produced  in  close  contact  with  the  ore.  Attempts  have 
been  made  to  reduce  the  ore  in  some  form  of  blast  furnace,  but 
the  zinc  was  too  easily  oxidized  by  the  furnace  gases,  and  it  was 
not  possible  to  condense  the  zinc  to  the  liquid  state,  as  the  vapor- 
ized metal  was  in  a  very  diluted  condition  in  the  gases 
leaving  the  furnace.  Zinc  oxide  suitable  for  making  paint  is, 
however,  produced  by  means  of  small  blast  furnaces,  and  is 
filtered  out  of  the  gases  by  passing  them  through  w^oolen  bags. 

In  the  electric  furnace,  heat  can  be  produced  without  the 
necessity  of  blowing  air  into  the  charge  ;  the  atmosphere  in  the 
furnace  can  be  made  thoroughly  reducing,  so  that  no  zinc  will  be 
oxidized,  and  the  gases  leaving  the  furnace  are  no  more  than 
leave  the  zinc  retort  in  the  usual  process,  so  that  the  condensa- 
tion of  the  zinc  should  be  satisfactory.  The  production  of  heat 
electrically,  in  the  midst  of  the  ore  mixture,  enables  the  furnace  to 
be  made  of  any  convenient  size,  and  thus  reduces  greatly  the  ex- 
pense of  labor,  while,  as  the  heat  has  not  to  be  transmitted  through 
the  furnace  walls,  these  will  be  far  more  permanent  and  a  great 
source  of  expense  will  thus  be  removed. 


'J.    W.    Richards'   Metallurgical    Calculations,    Part    I.,    p.    80 


ZIXC      SMELTING.  157 

Although  the  advantages  that  could  be  gained  by  smelting 
zinc  ores  electrically  were  very  obvious,  the  practical  application 
of  electrical  heating  to  this  process  has  not  been  easy.  The  first 
electrical  furnace  for  distilling  zinc  ores  was  patented  by  the 
Cowles  brothers  in  1885,  and  consisted,  Fig.  42,  of  a  fire-clay 
tube,  A,  closed  at  one  end  by  a  carbon  plug,  B,  and  at  the  other 
end  by  a  carbon  crucible,  C,  and  lid,  D.  The  charge  of  roasted 
ore  and  coal  was  contained  in  the  tube,  and  electrical  connections 
were  made  to  the  carbon  plate  and  crucible  so  that  an  electric 
current  flowed  through  and  heated  the  ore  in  the  tube.  The  tube 
was  surrounded  with  some  suitable  material  to  reduce  the  loss  of 
heat.  The  vaporized  zinc  and  other  gaseous  products  of  the  pro- 
cess escaped  through  a  hole  into  the  crucible,  where  the  zinc  con- 
densed to  a  liquid  at  Z,  while  the  remaining  gases  passed  away 
by  the  pipe  E.  The  furnace  was  practically  an  electrically  heated 
zinc  retort,  and,  as  shown  in  the  figure,  the  process  was  intended 
to  be  intermittent  in  action,  one  charge  being  exhausted  and  then 


B 


Fig.  42. — Cowles'  Electric  Zinc  Furnace. 

discharged  before  another  could  be  introduced.  Provision  could, 
however,  have  been  made  for  the  continuous  charging  and  dis- 
charging of  such  a  furnace,  but  the  process  was  never  com- 
pleted. 

A  furnace  recently  patented  by  \V.  McA.  Johnson,*  of  the 
Lanyon  Zinc  Co.,  Fig.  43,  is  practically  the  same  as  the  Cowles' 
furnace,  but  it  is  designed  on  a  larger  scale,  and  care  has  been 
taken  to  prevent  the  overheating  of  the  walls  of  the  furnace.  It 
consists  of  an  arched  chamber,  A,  \vith  end  walls,  B  and  C,  and  a 
fiue,  D,  through  which  the  zinc  and  other  gaseous  products  of  the 
operation  can  pass.  The  whole  furnace  is  supported  upon  I 
beams,  thus  enabling  the  air  to  pass  underneath  and  prevent  over- 
heating. The  furnace  is  constructed  of  fire-clay  bricks,  but  as 
additional  protection,  a  layer,  M,  of  refractory  material,  such  as 
silica,  high-grade  fire-clay  or  bauxite,  is  placed  on  the  hearth. 
The  ore  mixture  consists  of  roasted  ore  mixed  with  enough  coke  to 


*W.    McA.     Johnson,    Electric     Zinc    Furnace,    U.S.    patent    814,050,    filed    May    24th. 
1904,    Electrochemical    Industry,    vol.     iv.,    p.     152. 


158  THE     ELECTRIC     FURNACE. 

reduce  the  zinc  and  to  carry  the  electric  current.  Some  of  the 
ore  to  be  treated  contains  considerable  amounts  of  iron,  lime, 
lead  and  copper,  and  would  be  likely  to  flux  the  walls  of  the 
furnace.  This  low-grade  ore  is,  therefore,  placed  in  the  middle 
and  upper  part  of  the  furnace  at  K,  being  separated  from  the 
floor  and  walls  by  a  layer  of  purer  ore,  J.  All  the  ore  is  mixed 
with  enough  coke  to  reduce  the  zinc  it  contains,  but  in  order  to 
prevent  the  overheating  of  the  walls  care  is  taken  that  the  mixture 
K  shall  be  a  better  electrical  conductor  than  the  mixture  J,  so 
that  the  current  will  pass  mainly  through  the  middle  of  the 
furnace.  E  and  F  are  heaps  of  coke  serving  as  electrodes,  the 


Fig.  43. — Johnson's  Electric  Zinc  Furnace. 

current  flowing  between  E  and  F  through  the  ore  mixture.  Elec- 
trical contact  is  made  with  the  coke  by  means  of  graphite  or 
carbon  blocks  and  rods  passing  through  the  front  and  back  of 
the  furnace.  G  and  H  are  connected  to  one  cable  bringing  the 
current,  and  make  contact  with  the  coke  F,  while  two  similar 
terminals  connect  the  other  cable  to  the  coke  E.  This  furnace  is 
the  same  in  principle  as  an  ordinary  zinc  retort,  but  the  produc- 
tion of  the  necessary  heat  within  the  retort,  which  can  only  be 
effected  electrically,  enables  the  dimensions  of  the  retort  to  be  in- 
creased to  any  desirable  extent,  and  the  walls,  instead  of  being 
thin,  as  was  necessary  when  the  heat  had  to  pass  through  them, 
can  be  made  of  any  suitable  thickness.  The  furnace  is  neces- 
sarily intermittent  in  action,  and  would  be  allowed  to  cool  some- 
what to  allow  of  the  spent  ore  being  removed  through  some  con- 
venient opening  and  a  fresh  charge  being  carefully  arranged  in 
the  furnace  before  it  could  be  again  heated.  The  zinc  vapors 
passing  through  the  flue  D  would  enter  a  system  of  condensing 
chambers,  the  first  section  of  which  would  be  kept  at  a  tempera- 
ture above  the  melting  point  of  zinc  in  order  to  obtain  that  metal 
in  the  molten  condition. 

The  electric  zinc  furnace  of  C.  P.  G.  de  Laval,  Fig.  44,  was 
patented  some  years  ago,  and  has  this  advantage  over  the  John- 


ZINC      SMELTING. 


'59 


son  furnace,  that  the  ore  mixture  can  be  continually  charged  into 
the  furnace,  and  that  the  residues  are  fused  and  can  be  tapped 
out  at  intervals  without  interrupting  the  operation  of  the  furnace. 
The  heating  is  effected  by  an  arc  which  is  maintained  between  two 
carbon  electrodes,  one  of  which  is  shown  at  E.  The  ore  mixture 
is  introduced  continuously  by  means  of  a  charging  shaft,  A,  or 
by  a  hopper  and  screw  feed  through  the  wall,  F,*  and  forms  a 
heap,  C,  in  the  furnace,  where  it  is  gradually  heated,  the  zinc 
reduced  to  the  metallic  state  and  distilled,  and  the  residues  finally 


Fig.  44. — Laval's  Electric  Zinc  Furnace. 

melted  by  the  heat  of  the  arc.  The  vaporized  zinc  and  the  gases 
produced  by  the  action  of  the  coal  on  the  ore,  escape  by  a  pas- 
sage, D,  to  condensing  chambers,  where  the  zinc  is  obtained  in 
the  liquid  state.  The  heaping  up  of  the  ore  in  the  furnace  serves 
to  protect  the  charging  aperture  and  the  gradual  heating  of  the 
ore  is  probably  an  important  feature  of  the  process,  as  it  allows 
the  zinc  oxide  to  be  reduced  to  the  metallic  state,  and  the  result- 
ing zinc  to  escape  from  the  ore  before  fusion  sets  in,  as  it  is 
difficult  to  liberate  the  metal  from  its  ore  when  in  a  pasty  or 
fused  state.  The  utilization  of  the  electrical  heat  in  this  furnace 
is  not  perfect,  but  the  operation  is  simple,  and,  therefore,  not 
likely  to  give  trouble.  Information  with  regard  to  the  actual 
working  of  the  furnace  is  not  available,  so  that  it  is  impossible 


*C.   G.    P.  De  Laval,  U.S.   patent  768,054,  Electrochemical  Industry,  vol.  ii.,  p. 


i6o 


THE     ELECTRIC     FURNACE. 


to  say  exactly  how  much  power  is  needed  to  reduce  the  zinc,  how 
perfectly  the  zinc  is  extracted  from  the  ores,  or  how  completely 
the  distilled  zinc  condenses  to  the  liquid  state.  The  process  has 
been  in  operation  commercially  for  several  years  in  Europe,  where 
three  plants  are  now  in  operation.  Three  thousand  horse-power 
is  employed  at  Trollhattan  (Sweden)  in  the  reduction  of  ore  and 
zinc  ashes  (galvanizers'  waste),  4,000  horse-power  at  Sarpsborg 


Fig.  45. — Salgues'   Electric  Zinc  Furnace. 

(Norway)  in   the  reduction  of  zinc  ashes,  and   1,800  horse-power 
?,t  Hallstaharnmar  in  the  smelting"  of  ore.* 

M.  A.  Sal-guest  wrote  an  account  of  the  electro-metallurgy  of 
zinc,  and  figured  two  or  three  furnaces,  one  of  which,  intended 
for  use  with  100  kilowatts,  is  illustrated  in  Fig.  45.  It  consists 
of  a  chamber,  built  in  two  parts,  A  and  R,  to  facilitate  cleaning 


*Report    of    the   Commission    t-i    investigate    the    zinc    r 
id    the    conditions    affecting    their    exploitation,    Otta\va, 
fSal-ucs    Bull,    Soc.     In-r.    Civ.,    1903,    p.     17.]. 


)f    British    Columbia 


ZINC      SMELTING.  l6l 

and  repairing,  an  off-take,  C,  for  the  passage  of  the  zinc  and 
other  gases,  a  tap-hole,  D,  and  two  charging  and  poking  holes, 
one  of  which  is  shown  at  E.  Heat  is  produced  in  the  charge  of 
ore  by  the  passage  of  a  current  between  the  carbon  electrodes, 
F  and  G,  F  being  movable  and  supported  by  a  suitable  carbon 
holder,  while  G  is  set  in  the  base  of  the  furnace,  and  electrical 
contact  is  made  with  it  by  the  bar  of  metal,  H.  The  furnace  is 
built  of  firebricks  inside  an  iron  jacket,  which  is  cooled  by  sprink- 
lers shown  at  K,  the  lower  carbon  holder  having  a  special  water- 
cooling  device,  shown  at  L.  The  hearth  of  the  furnace  is,  how- 
ever, lined  with  sand,  J,  as  is  common  in  many  smelting  furnaces. 

Salgues  draws  special  attention  to  the  means  by  which  he 
keeps  the  furnace  air-tight  around  the  upper  carbon  and  at  the 
poking  and  charging  holes.  For  this  purpose  he  provides  a 
heavy  cast  iron  plate,  M,  in  which  are  holes  for  the  electrode  and 
for  charging,  the  latter  being  closed  by  lids,  O.  The  gases  in  the 
furnace,  being  under  a  slight  pressure,  rush  out  through  any 
opening,  such  as  the  crack  around  the  electrode,  but  a  ring  of 
asbestos,  N,  delays  the  gases  a  little,  and  the  zinc  vapor  will 
then  condense  on  the  iron  plate  (which  is  cooled  by  a  jet  of  water), 
and  immediately  closes  the  crack.  In  the  same  way,  after 
charging  or  poking,  the  crack  between  the  lid,  O,  and  its  seat  is 
immediately  sealed  by  the  zinc,  which  condenses  there. 

The  charge,  consisting  of  roasted  ore  and  the  necessary  car- 
bon for  its  reduction,  being  introduced  at  E,  from  time  to  time, 
lies  around  the  carbon,  F,  and  as  it  becomes  heated  the  zinc  is 
reduced  and  volatilized,  passing  through  C  to  condensing  cham- 
bers ;  while  the  residue  of  the  ore,  which  would  need  to  be  fusible, 
collects  in  the  molten  state  at  R,  and  is  tapped  out  at  intervals. 
This  furnace  is  continuous  in  operation,  and  incidentally  allows 
of  the  smelting  of  associated  metals,  such  as  lead,  which  will 
collect  in  the  furnace  and  be  tapped  out  with  the  slag.  The  heat 
may  be  produced  in  this  furnace  by  the  passage  of  the  current 
through  the  molten  slag,  R,  but  if  the  electrode,  F,  were  raised 
higher  an  arc  would  be  produced.  Salgues  experimented  at 
Champagne  (Ariege),  France,  with  a  modified  carbide  furnace  of 
100  kilowatts,  and  using  ores  carrying  40  to  45  per  cent,  of  zinc, 
fed  cold  into  the  furnace,  he  obtained  a  yield  of  5  kg.  of  zinc 
(probably  zinc  dust)  per  kilowatt  day. 

A  notable  defect  in  the  electric  smelting  of  zinc  ores  is  the 
difficulty  experienced  in  attempting  to  obtain  the  distilled  zinc 
in  the  liquid  state.  In  the  older  processes  a  large  proportion  of 
the  zinc  condenses  as  a  liquid  in  the  clay  condensers,  which  are 


l62  THE     ELECTRIC     FURNACE. 

fitted  to  the  end  of  each  retort,  and  are  hot  enough  to  keep  the 
metal  liquid,  a  small  portion  passing  on  to  the  cooler  "prolong" 
and  condensing  in  this  as  a  metallic  powder ;  but  the  electric 
furnace  makes  very  little  liquid  zinc,  nearly  all  being  in  the  state 
of  powder.  The  explanation  of  this  is  probably  that  in  the  older 
process  the  ore  was  heated  very  gradually  in  the  retort,  and  the 
reduction  of  oxide  to  metal  was  partly  completed  before  the  zinc 
began  to  distil  from  the  retort.  In  this  way  the  carbon  mon- 
oxide, moisture  and  other  products  of  the  ore  and  the  coal  had 
been  partly  driven  off  before  the  distillation  began,  and  the  zinc 
vapors  were  in  consequence  more  concentrated,  and  condensed 
more  readily  to  the  liquid  state. 

The  conditions  for  the  production  of  liquid  or  powdery  zinc 
will  be  seen  at  once  when  it  is  remembered  that  the  former  cor- 
responds to  rain  and  the  latter  to  hoar-frost  or  snow.  A  hot, 
moist  wTind  being  cooled  to  some  temperature  above  the  freezing 
point  will  form  rain,  while,  if  the  air  is  so  dry,  that  is,  the  water 
vapor  is  so  dilute,  that  the  air  must  be  cooled  below  the  freezing 
point  before  saturation  occurs,  hoar-frost  or  snow  will  result.  Be- 
sides this  general  consideration  there  is  the  need  of  time,  and 
points  on  which  the  precipitation  may  occur ;  the  slow  distillation 
in  the  older  retorts  would,  therefore,  be  more  favorable  to  the 
condensation  of  zinc  than  the  rapid  work  of  an  electric  furnace, 
with  a  rush  of  gas  carrying  the  zinc  vapor  into  the  colder  parts 
of  the  condenser  before  the  metal  has  had  time  to  condense  into 
drops.  Salgues  describes  an  arrangement  for  condensing  the 
zinc  in  the  powdery  form  in  a  series  of  tubes,  the  zinc  being  pro- 
tected from  oxidation  and  re-distilled  in  an  auxiliary  furnace,  in 
which,  as  the  vapor  is  quite  concentrated,  liquid  zinc  can  be  ob- 
tained. 

It  is  in  the  smelting  of  mixed  ores  containing  both  zinc  and 
lead,  usually  associated  with  silver,  that  the  greatest  advantage  of 
electrical  smelting  may  be  expected.  Such  ores  are  very  difficult 
to  treat  by  ordinary  furnace  methods,  because,  if  smelted  as  a 
lead  ore  in  the  blast  furnace,  the  zinc  makes  infusible  slags  and 
chokes  up  the  furnace  with  deposits  of  fume,  and  none  of  the  zinc 
Is  recovered.  If  treated  as  a  zinc  ore,  the  lead  makes  the  ore 
fusible  so  that  it  corrodes  the  retorts,  besides  yielding  an  impure 
zinc  containing  some  lead.  When  treated  as  a  zinc  ore,  the  lead 
and  silver  can  be  recovered  by  smelting  the  residues  from  the 
zinc  retorts. 

The  Broken  Hill  ores  are  notable  examples  of  a  mixed 
sulphide  of  lead  and  zinc  which  cannot  be  separated  at  all  com- 


ZIXC     SMELTING. 


Fig.  46. — Experimental  Zinc  Furnace. 


164  THE     ELECTRIC     FURNACE. 

pletely  by  mechanical  means  and  must  be  treated  as  a  whole  by 
smelting  or  chemical  methods.  It  occurred  to  the  writer  several 
years  ago  that  such  ores  could  be  smelted  electrically  so  as  to  re- 
cover at  one  operation  the  zinc,  lead  and  silver  from  the  ore  ;  the 
zinc  being  distilled  and  condensed,  while  the  lead  carrying  the 
silver  from  the  ore,  would  collect  in  the  molten  condition  as  in 
ordinary  blast  furnace  practice.  Numerous  experiments  on  a 
laboratory  scale  showed  that  this  could  be  accomplished,  and  that 
the  extraction  of  the  lead  was  particularly  good,  only  traces  of 
that  metal  remaining  in  the  slag. 

The  furnace  in  which  these  experiments  were  made  is  shown 
ir.  Fig.  46.*"  It  consisted  of  a  rectangular  chamber,  AB,  in  which 
the  ore  was  smelted,  a  charging  shaft,  C,  for  introducing  the  ore, 
and  chambers,  F  to  K,  for  condensing  and  collecting  the  zinc. 
The  electric  current  was  introduced  by  means  of  the  carbon 
electrodes,  D  and  E,  which  dipped  into  the  molten  slag  in  the 
furnace.  In  starting,  a  quantity  of  slag  was  melted  and  poured 
into  the  furnace  which  had  previously  been  heated.  The  elec- 
trodes were  then  introduced,  and  the  current  switched  on.  The 
mixture  of  roasted  ore,  carbon  and  fluxes  was  poured  into  the 
shaft,  C,  which  was  kept  nearly  full  during  the  operation  of  the 
furnace.  The  furnace  was  essentially  a  resistance , furnace,  the 
heating  being  accomplished  by  the  passage  of  the  current  through 
the  molten  slag,  and  the  furnace  was  made  long  and  narrow  in 
order  that  the  electrical  resistance  might  not  be  too  low. 
Occasionally,  however,  the  electrodes  would  become  too  short 
to  reach  the  slag,  and  an  arc  was  then  formed.  The  products  of 
the  operation  were  lead,  which  collected  at  L,  and  was  tapped  out 
by  the  spout,  R,  slag  which  is  shown  at  S,  and  was  tapped  out  by 
the  spout,  T,  and  zinc  vapor  and  other  gases  which  left  the 
furnace  by  the  openings  FF.  The  condensing  system  consisted 
of  the  chamber,  F,  in  which  a  small  amount  of  molten  zinc  col- 
lected, and  an  extensive  system  of  iron  pipes,  GH,  and  JK,  in 
which  the  greater  part  of  the  zinc  collected  in  the  form  of  zinc 
powTder.  The  gases  escaping  with  the  zinc  vapor  were  mostly 
carbon  monoxide  which  burned  at  the  end  of  the  condensing 
system. 

The  cost  of  smelting  sulphide  ores  of  zinc  is  materially  in- 
creased by  the  necessity  of  a  very  complete  roasting  operation 

This   furnace    was    devised    by    the    author    and    Mr.    L.    B.    Reynolds,    who    did    most 
of    the     experimental     work.  They     have    obtained     the    following     patents     on     the 

electrical  smelting  of  lead-zinc:  oAs  : — Canadian  102,231,  Australian  1,681,  German 
185,470,  Mexican,  4,710. 


ZIXC      SMELTING.  165 

before  the  distillation  of  the  zinc.  Any  sulphur  left  in  the  ore 
to  be  treated  by  the  ordinary  process  holds,  as  a  rule,  about  twice 
its  weight  of  zinc  in  the  residues,  and  it  is,  therefore,  the  practice 
to  leave  no  more  than  about  one  per  cent,  of  sulphur  in  the 
roasted  ore.  So  complete  a  removal  of  sulphur  involves  a  pro- 
longed roasting  at  a  very  high  temperature,  thus  largely  increas- 
ing the  cost  as  well  as  the  loss  by  volatilization  of  the  lead  and 
silver  in  the  ore.  Some  inventors  have  tried  to  avoid  this  by 
smelting  the  ore,  unroasted,  in  the  electric  furnace,  with  the 
addition  of  some  reagent  for  absorbing  the  sulphur ;  iron, 
iron  ore,  alkaline  salts  and  lime  being  suitable  for  this 
purpose. 

F.  T.  Snyder,  of  the  American  Zinc  Extraction  Co.,  has 
patented*  a  process  for  obtaining  zinc  from  a  sulphide  ore  of  this 
metal  without  roasting.  The  ore  is  mixed  with  carbon  and  fluxes 
(iron  and  lime),  and  smelted  upon  a  bath  of  molten  slag  in  an 
electric  furnace  from  which  the  air  is  excluded.  The  inventor 
claims  that  the  carbon  reacts  with  the  sulphur  of  the  ore  and 
forms  carbon  bisulphide,  which  is  volatilized,  liberating  the  zinc. 
It  is  not  stated  whether  the  iron  and  lime  used  as  fluxes  played 
any  part  in  absorbing  the  sulphur  and  liberating  the  zinc.  Direct 
current  is  used,  and  some  electrolytic  effect  takes  place,  as  the 
zinc  is  liberated  at  one  electrode  and  the  carbon  bisulphide  at  the 
other  electrode.  The  two  vapors  can,  therefore,  be  kept  apart 
and  the  zinc  vapor,  being  undiluted,  should  be  easily  condensed. 
Even  if  the  two  vapors  could  not  be  kept  separate,  the  amount  of 
carbon  bisulphide  formed  would  only  be  about  half  as  much  as  the 
carbon  monoxide  that  would  have  been  formed  if  the  ore  had  first 
been  roasted,  and,  therefore,  the  zinc  vapor  would  be  more  con- 
centrated and  likely  to  condense  better. 

In  an  experiment,  ore  containing  20  per  cent,  zinc,  20  per 
cent,  iron,  5  per  cent,  lead,  35  per  cent,  sulphur,  and  20  per  cent, 
of  silica  and  alumina  was  mixed  with  iron  and  lime  (and  carbon) 
and  fed  into  an  electric  furnace  provided  with  carbon  electrodes, 
between  wrhich  scrap  lead  had  been  placed  for  starting  the  furnace. 
A  direct  current  of  1,500  to  1,800  amperes  at  7  to  15  volts  was 
employed,  heating  the  furnace  to  about  i,2oo°C.  The  ore  melted 
and  was  reduced,  zinc  being  liberated  in  the  form  of  vapor  near 
one  electrode,  while  carbon  bisulphide  was  formed  near  the  other 
electrode.  It  is  claimed  that  at  least  94  per  cent,  of 
the  zinc  in  the  charge  can  be  recovered  by  this  pro- 
cess. 


*F.   T.   Snyder,  U.S.   patent  814,810,  filed  June  ajrd,   1905,   Electrochemical  Industry, 
rol.  iv.,  p.  152. 

12 


T  66 


THE    ELECTRIC    FURNACE. 


Fig.  47. — Snyder's  Induction  Furnace, 


ZINC      SMELTING.  1 67 

Mr.  Snyder  has  experimented  with  induction  furnaces  for 
smelting  zinc  and  other  ores.  The  furnace  represented  in 
Fig.  47*  being  intended  for  ores  in  general,  while  a  zinc-smelting 
furnacet  would  be  provided  with  chambers  for  condensing  the 
zinc.  The  furnace  shown  in  Fig.  47,  which  could  be  used  for 
smelting  lead  ores,  has  a  laminated  iron  core,  CC,  a  pair  of 
primary  coils,  PP,  and  a  secondary  circuit  made  up  of  the  molten 
slag,  S,  the  molten  metal,  MM,  and  bars,  N,  of  copper  or  some 
other  metal  which  should  not  be  attacked  by  the  molten  metal,  M. 
The  alternating  current  in  PP,  supplied  by  the  dynamo,  D,  causes 
a  much  larger  low-voltage  current  to  flow  around  the  secondary 
circuit,  N  M  S  M  N,  composed  of  the  copper  bars,  N,  the  molten 
metal,  M,  and  the  molten  slag,  S.  As  the  slag  has  a  higher 
electrical  resistance  than  the  other  parts  of  this  circuit,  the  greater 
part  of  the  heat  will  be  developed  in  it,  and  the  ore  introduced 
through  the  hoppers  will  be  heated,  reduced  and  melted  by  con- 
tact with  the  super-heated  slag.  The  iron  core,  CC,  passes 
through  the  middle  of  the  furnace,  and  is  therefore  provided  with 
water-cooling  devices,  not  shown  in  the  drawing,  to  avoid  over- 
heating. 

Mr.  Snyder's  latest  zinc  furnacet  is  shown  in  Fig.  48.  It 
is  designed  for  the  treatment  of  lead-zinc  ores,  with  the  special 
intention  of  obtaining  the  resulting  zinc  in  a  coherent  liquid  state, 
instead  of  in  the  form  of  a  powder.  The  furnace  is  constructed 
on  the  lines  of  a  lead  blast-furnace,  having  a  wrater-jacketed  smelt- 
ing shaft,  bb,  and  a  crucible  aa,  holding  the  molten  lead  and 
molten  slag  produced  in  the  operation.  A  siphon  tap,  O,  en- 
ables the  molten  lead  to  flow  out  of  the  furnace,  and  the  slag  and 
matte  formed  are  tapped  out  through  the  hole,  1.  The  special 
feature  for  obtaining  liquid  zinc  is  the  provision  of  the  water- 
jackets,  bb,  and  of  channels,  gg,  at  the  bottom  of  the  water- 
jackets.  The  charge  contains  partly  roasted  ore,  carbon  and 
fluxes,  and  as  it  descends  in  the  furnace,  the  zinc  and  other  metals 
are  reduced  to  the  metallic  state,  and  gases  such  as  carbon 
monoxide  are  liberated.  A  part  of  these  gases  is  liberated  in  the 
upper  and  cooler  part  of  the  shaft,  so  that  the  zinc  vapor,  which 
is  not  formed  until  the  ore  reaches  the  hotter  part  near  the  bottom 


'Induction  furnace,  F.  T.  Snyder,  U.S.  patent  825,359.  Application  filed  July  isth, 
1904.  See  Electrochemical  Industry,  vol.  iv.,  p.  319. 

•f-Induction  Furnace  fcr  Zinc,  F.  T.  Snyder,  U.S.  patent  859,134.  See  Electro- 
chemical Industry,  vol.  v.,  p.  323. 

tDrawing  and  description  sent  to  the  author  by  Mr.  Snyder.  Compare  F.  T. 
Snyder  U.S.  patent  859,133.  See  Electrochemical  Industry,  vol.  v.,  p.  323. 


i68 


THE    ELECTRIC    FURNACE. 


Fig.  48. — Snyder's  Furnace  for  Obtaining  Liquid  Zinc. 


ZINC      SMELTING.  169 

of  the  shaft,  is  less  diluted  by  permanent  gases  than  it  would  be  if 
the  zinc  and  the  gases  were  all  liberated  in  a  common  chamber 
as  would  be  the  case  in  Fig.  47.  The  zinc  vapor  passes  up  the 
shaft,  with  the  other  gases,  but  on  reaching  the  cooler  parts  of 
the  ore,  it  is  largely  condensed  in  the  ore,  and  passes  down  again 
with  the  descending  ore  to  the  hotter  parts  of  the  furnace.  The 
result  of  this  process  is  that  the  zinc  vapor  becomes  concentrated 
in  the  lower  part  of  the  furnace,  and  finally  begins  to  condense  in 
the  liquid  state  in  the  vicinity  of  the  water-cooled  walls,  bb. 
The  condensation  of  the  zinc  vapor  occurs  more  freely  at  the 
sides  of  the  furnace  than  at  the  ends,  since  the  former  are  further 
from  the  carbon  electrodes,  and  are  therefore  cooler.  The  con- 
densed zinc  flows  out  of  the  furnace  through  the  channels,  gg, 
beneath  the  sides  of  the  furnace,  and  collects  at  hh.  The  molten 
materials  in  the  bottom  of  the  furnace  are  lead,  L,  matte,  M,  and 
slag,  S.  The  slag  becomes  congealed  around  the  sides  and 
ends  of  the  furnace,  and  in  this  way  maintains  the  channel 
through  which  the  zinc  flows.  This  is  possible  because  zinc  melts 
at  4i9°C.  whilst  the  slag  will  remain  solid  up  to  at  least  i,ooo°C. 
The  solidified  slag  also  serves  to  prevent  any  leakage  of  the  cur- 
rent by  passing  through  the  molten  slag  into  the  metal  of  the 
water-jacket.  Such  leakage  could  take  place,  however,  higher  up 
in  the  furnace  \vhere  there  is  no  slag  to  form  a  crust  on  the 
iron. 

Another  feature  of  interest  is  the  arrangement  for  using  three- 
phase  current.  The  inventor  has  adopted  the  system  explained 
in  chapter  v. ,  Fig.  35,  in  which  three  electrodes,  or  some  multiple 
of  this,  are  employed  and  are  connected  to  the  transformers  in 
such  a  way  that  the  current  entering  by  any  electrode  returns 
through  the  other  two,  thus  rendering  unnecessary  the  three  re- 
turn cables  shown  in  Fig.  33  and  Fig.  34.  A  single  return  cable 
from  the  molten  lead  in  the  furnace  is  provided  to  carry  any  un- 
balanced current.  This  arrangement  avoids  the  difficulty  that 
would  arise  from  the  inductive  effect  of  the  iron  jackets  if  the 
current  passed  completely  through  them,  entering  the  furnace 
by  the  electrodes,  cc,  and  leaving  by  a  connection  from  the 
crucible,  aa,  as  in  the  Heroult  furnace,  Fig.  29. 

In  smelting  a  sulphide  ore  of  lead  and  zinc  in  this  furnace, 
it  is  first  roasted  until  it  contains  about  8%  of  sulphur  and  then 
smelted  in  admixture  with  coke  or  charcoal  and  fluxes.  The 
charge  is  proportioned  so  that  the  resulting  slag  will  be  high  in 
lime  and  silica,  (at  least  50%  of  the  latter),  as  such  a  slag  will 
not  retain  any  considerable  quantity  of  zinc,  on  account  of  its 


170  THE     ELECTRIC     FURNACE. 

high  melting  temperature,  and  will  have  a  high  electrical  resist- 
ance. A  considerable  amount  of  matte  is  preferred,  enough 
iron  being  present  in  the  charge  to  prevent  much  of  the  zinc- 
entering  the  matte. 

This  furnace  has  been  described  at  length,  as  being  the  first 
electrical  zinc  furnace  in  which  any  rational  attempt  has  been 
made  to  obtain  the  zinc  in  the  liquid  state.  The  author  would 
anticipate  certain  difficulties  in  the  operation  of  such  a  furnace, 
such  as  the  formation  of  crusts  of  zinc  in  the  shaft,  which  would 
prevent  the  regular  descent  of  the  charge  and  the  passage  of 
the  furnace  gases. 

With  regard  to  the  amount  of  electrical  energy  required  to 
smelt  a  ton  of  roasted  zinc  ore  the  following  data  may  be  given. 
Salgues  states  that  from  a  40  or  45  per  cent,  ore  he  extracted  5 
kg.  of  zinc  per  kilowatt  day.  This  would  correspond  to  1,660 
kilowatt  hours  per  2,000  pounds  of  zinc  ore  if  the  zinc  obtained 
amounted  to  38  per  cent,  of  the  ore.  Casaretti  and  Bertani*  pro- 
duced at  Bergamo,  Italy,  9  kg.  of  zinc  per  kilowatt  day,  which, 
on  a  zinc  extraction  of  38  per  cent,  of  the  ore,  would  mean  920 
kilowatt  hours  per  2,000  pounds  of  ore.  The  author,  using  a 
mixed  lead  zinc  ore  carrying  about  25  per  cent,  of  each  metal,  was 
able  to  extract  both  metals  with  an  expenditure  of  from  800  to  850 
kilowatt  hours  per  2,000  pounds  of  ore,  using  the  ore  cold,  and 
in  a  small  furnace  of  only  15  kilowatts.  Snydert  has  made  a 
calculation  based  partly  on  the  fuel  needed  in  blast  furnace  lead 
smelting  and  partly  on  the  heat  theoretically  needed  to  reduce  and 
distil  zinc  from  its  ores,  and  gives  the  formula,  623  +  5.4  times 
the  percentage  of  zinc,  for  the  kilowatt  hours  needed  per  2,000 
pounds  of  a  lead  zinc  ore.  From  the  above  data  it  may  be  fairly 
inferred  that  smelting  mixed  lead  zinc  ores  in  large  electrical 
furnaces  would  take  less  than  800  kilowatt  hours,  while  for  ores 
running  higher  in  zinc,  say  40  to  50  per  cent.,  about  900  kilo- 
watt hours  would  be  needed.  These  figures  correspond  to  the 
treatment  of  the  cold  ore  which  had  previously  been  roasted  to 
remove  the  sulphur;  if  the  ore  could  be  charged  hot  from  the 
roasting  furnace,  or  if  the  carbon  monoxide  resulting 
from  the  smelting  operation  could  be  used  to  pre- 
heat the  ore,  a  decidedly  lower  figure  should  be  suf- 
ficient. 


*Casaretti   and  Bertani,  Report  of  Commission   on    zinc   resources    of  British   Colum- 
bia,   1906,   p.    131. 

fSnyder,    Journ.    Can.   Min.    Inst.,   vol.    viii.,    1905,    p.    130. 


MISCELLANEOUS      USES.  171 

IV. — Miscellaneous  Uses  of  the  Electric  Furnace. 

Silicon. — It  has  been  estimated  by  Dr.  F.  W.  Clarke*  that 
silicon  forms  27.4%  of  the  contents  of  the  solid  crust  of  the 
earth.  It  exists  in  combination  with  oxygen,  as  silica  which 
constitutes,  according  to  this  estimate,  58.3%  of  the  earth's  crust. 
Although  so  widely  distributed,  silicon  has  so  strong  an 
affinity  for  oxygen  that  until  recently  it  could  only  be  obtained 
in  small  amounts. 

Alloyed  with  certain  metals,  silicon  has  long  been  of 
metallurgical  importance.  Ferro-silicon,  already  referred  to,  has 
been  employed  in  the  manufacture  of  steel  as  a  deoxidizer  and  to 
prevent  the  formation  of  blow-holes  in  steel  ingots.  Cast  iron 
contains  a  small  amount  of  silicon,  which  has  a  very  great  effect 
on  the  properties  of  the  iron. 

Silicon  has  been  obtained  in  the  electric  furnace  by  the  action 
of  carbon  on  silica,  but  it  is  not  easy  to  obtain  silicon 
in  this  manner  because  it  is  volatile  at  the  temperature 
of  the  reaction.  Mr.  F.  J.  Tone  has  overcome  this  difficulty  and 
has  produced  considerable  quantities  of  silicon  using  at  first  the 
furnace  shown  in  Fig.  15,  p.  25.  More  recently  he  has  employed 
B  furnace  like  the  Heroult  steel  furnace  for  the  production  of 
silicon  and  its  alloys. t  The  production  of  silicon  in  the  electric 
furnace  has  been  described  by  F.  J.  Tone,t  who  also  gives  an 
account  of  its  properties  and  uses.  Silicon  produced 
in  the  electric  furnace  is  a  brittle  crystalline  body  with  a 
dark  silver  luster.  Its  specific  gravity  is  2.34  and  it  melts  at 
i,43o°C.  It  is  not  pure,  however,  but  contains  about 
i  %  of  iron,  i  J-a  %  of  aluminium,  and  2%  of  carbon. 

The  heat  of  oxidation  of  silicon  has  been  determined  by  Dr. 
H.  X.  Potter, §  who  gives  215,692  calories  as  the  heat  formation 
of  one  gram  molecule  of  silica.  Using  this  figure  it  can  be  shown 
that  the  oxidation  of  silicon  affords  more  heat  per  unit  weight 
of  oxygen  than  the  oxidation  of  any  of  the  metals  except 
aluminium  and  the  alkaline  earth  metals  such  as  magnesium  and 


*Dr.  F.  W.  Clarke,  of  the  United  States  Geological  Survey.  Quoted  in  Electro- 
chemical Industry,  vol.  iii.,  p.  409. 

•f-Production  of  Silicides  and  Silicon  Alloys.  F.  J.  Tone,  U.S.  patent  842,273;  see 
Electrochemical  Industry,  vol.  v.,  p.  141. 

^Production  of  Silicon  in  the  Electric  Furnace.  F.  J.  Tone,  Trans.  Amer.  Electro- 
chem.  Soc.,  vol.  vii.,  1905,  p.  243. 

§H.  N.  Potter,  Trans.  Amer.  Electrochem.  Soc.,  vol.  xi.,  abstracted  in  Electro- 
chemical Industry,  vol.  v.,  p.  229. 


172  THE  ELECTRIC  FURNACE. 

calcium.  The  great  affinity  of  silicon  for  oxygen  has  enabled  it 
to  be  used  for  the  reduction  of  metals  such  as  chromium 
and  tungsten  in  the  electric  furnace.*  Dr.  Goldschmidt  has 
stated  that  silicon  cannot  be  used  instead  of  aluminium  in  the 
thermit  mixtures  for  welding  and  the  production  of  carbon-free 
metals,  as  the  reaction  between  silicon  and  iron  oxides  is  not 
sufficiently  rapid.  It  is  claimed,  however,  that  Mr.  Albro  has 
succeeded  in  using  silicon  in  this  manner  ;t  the  mixture  of  silicon 
and  oxygen-supplying  compound  which  he  uses  being  called 
Calorite. 

Silicon-copper,  an  alloy  of  silicon,  is  used  as  a  de- 
oxidizer  in  making  castings  of  copper  and  copper  alloys,  in  the 
same  way  that  the  ferro-alloy  of  silicon  is  used  in  making  steel 
castings.  Copper-silicon  is  made  in  the  electric  furnace  by  the 
Cowles  Electric  Smelting  and  Aluminium  Company,  at  Lock- 
port,  N.Y4 

Fused  Quartz. — Silica,  the  oxide  of  silicon,  is  a  valuable  re- 
fractory material  for  lining  metallurgical  furnaces.  Its  uses  as  a 
refractory  material  have  been  described  in  Chapter  IV.  Although 
very  refractory,  silica  or  quartz  can  be  fused,  and  it  then 
possesses  valuable  properties,  and  has  been  used  for  some  time  in 
the  construction  of  scientific  apparatus.  As  an  example,  the 
well-known  quartz  filaments  of  C.  V.  Boys  may  be  mentioned. 
These  are  made  by  melting  the  quartz  in  the  oxyhydrogen  blow- 
pipe. Recently  it  has  been  found  possible  to  fuse  quartz  in  the 
electric  furnace  and  to  make  tubes,  crucibles,  dishes  and  other 
articles  out  of  the  fused  quartz.  This  material  scarcely  expands 
at  all  when  heated,  its  coefficient  of  expansion  being  only  one- 
twentieth  of  that  of  glass.  In  consequence  of  this  it  is  possible 
to  plunge  a  red-hot  article  made  of  fused  quartz  into  cold  water 
without  cracking  it.  Fused  quartz  is  a  transparent  glass,  but 
"Electroquartz"  or  silica  melted  in  the  electric  furnace  has  a 
milky  white  color.  Articles  of  this  material  can  be  obtained  from 
the  Wilson-Maeulen  Co.,  no  Liberty  Street,  New  York.§ 

Information  with  regard  to  the  manufacture  of  fused  quartz 
articles  in  the  electric  furnace  can  be  found  in  the  Electrochemical 
Industry,  vol.  iii.,  p.  53,  and  vol.  iv.,  pp.  369  and  502. 

Glass. — Although  glass  can  easily  be  melted  in  furnaces  fired 
by  gas,  the  cleanliness  and  convenience  of  electrical  heating  have 


*F.    M.   Becket,    patents    described   in    Electrochemical  Industry,   vol.    v.,   p.    237. 
•f-Trans.   Amer.    Electrochem.   Soc.,   vol.    vii.,   p.    249. 

tSilicon-copper  in    the    Brass   Foundry,    Electrochemical    Industry,   vol.    ii.,    p.    121. 
^Electrochemical    Industry,   vol.    v.,    pp.    67    and    107. 


MISCELLANEOUS      USES.  173 

led  to  the  use  of  the  electric  furnace  in  the  manufacture  of  glass. 
A  large  number  of  furnaces  have  been  devised  for  this  purpose 
and  particulars  of  some  of  these  will  be  found  in  Wright's 
book  on  Electric  Furnaces,  and  in  volumes  i.,  ii.,  and  iii.,  of 
the  Electrochemical  Industry. 

Alundum. — This  is  an  artificial  corundum  or  emery  made  by 
fusing  bauxite  in  an  electric  furnace,  and  allowing  it  to  cool 
slowly,  thus  forming  a  hard  and  tough  crystalline  mass  which  is 
broken  up  and  used  as  an  abrasive.  The  process  was  invented 
by  C.  B.  Jacobs,*  and  the  material  is  manufactured  at  Niagara 
Falls  by  the  Norton  Company,  t  An  electric  furnace  suitable  for 
the  manufacture  of  alundum  has  been  patented  by  A.  C. 
Higgins.t 

Nitric  Acid. — An  interesting  application  of  the  electric 
furnace  is  found  in  the  production  of  nitric  acid  from  air.  It  has 
been  known  for  a  long  time  that  an  electric  discharge  has  the 
property  of  causing  the  oxygen  and  nitrogen  of  the  air  to  com- 
bine together,  forming  nitric  oxide,  and  the  method  was  used  a 
number  of  years  ago  for  removing  nitrogen  from  air  and  so 
isolating  the  small  amount  of  argon  which  it  contained.  Many 
inventors  have  tried  to  find  a  method  of  producing  nitric  acid  or 
other  compounds  of  nitrogen  from  the  air  on  a  commercial  scale, 
and  by  one  process,  that  of  Birkeland  and  Eyde,§  calcium  nitrate 
is  now  produced  on  a  considerable  scale.  The  apparatus  con- 
sists of  a  disc-shaped  furnace,  lined  with  fire-brick,  in  which  an 
electric  arc  is  maintained  between  twro  water-cooled  copper 
electrodes  which  are  held  about  one  centimeter  apart.  An  alter- 
nating current,  at  about  5,000  volts,  is  employed  to  produce  the 
arc,  which  is  spread  out,  by  means  of  a  strong  electro-magnet, 
into  a  disc  of  flame  as  much  as  6^  feet  in  diameter.  This  im- 
mense arc  consumes  no  less  than  500  kilo\vatts,  and  even  larger 
furnaces  are  contemplated.  Air  is  passed  through  the  furnace, 
traversing  the  arc,  and  a  portion  of  the  nitrogen  combines  with 
oxygen  to  form  nitric  oxide,  of  which  about  2%  is  present  in  the 
issuing  air.  After  leaving  the  furnace  the  gases  pass  through 


*C.    B.    Jacobs,   U.S.    patent  659,926,   Electrochemical    Industry,   vol.    iii.,   p.   406. 

'J-Electrochemical  Industry,  vol.  i.,  p.  15. 

JA.    C.    Higgins,   U.S.    patent   775,654,    Electrochemical    Industry,    vol.    iii.,    p.    30. 

§The  manufacture  of  Nitrates  from  Air,  by  A.  J.  Lotka,  Chem.  Ind.,  1905,  p.  695, 
abstracted  in  Engineering  and  Mining  Journal,  1907,  p.  848. 

Electrical  Extraction  of  Nitrogen  from  the  Air,  by  J.  S.  Edstrom,  Trans.  Internat. 
Electrical  Congress,  St.  Louis,  1904,  vol.  ii.,  p.  17,  abstracted  Electrochemical  Industry, 
vol.  ii.,  p.  399. 

Electrochemical   Industry,    vol.    iv.,   pp.    126,    295,    and    360;   vol.    v.,    p.    358. 


174  THE     ELECTRIC     FURNACE. 

reaction  towers  in  which  the  nitric  oxide  combines  with  more 
oxygen  to  form  nitric  peroxide  and  this  unites  with  water  to  form 
nitric  acid.  The  acid  is  not  sold  in  that  form  but  is  neutralized 
with  limestone  yielding  calcium  nitrate  which  is  found  to  be  an 
excellent  fertilizer  as  well  as  forming1  a  raw  material  for  certain 
chemical  processes.  The  yield-  of  this  material  corresponds  to 
500  or  600  kilograms  of  pure  nitric  acid  per  kilowatt-year.  The 
industry  is  carried  on  at  Notodden  in  Norway,  where  the  operat- 
ing company  controls  water  falls  with  an  aggregate  of  350,000 
horse-power  which  can  furnish  electrical  energy  at  a  cost  of  about 
$3  per  horse-power-year. 

Phosphorus. — This  is  largely  made  in  the  electric 'furnace.  It 
is  obtained  by  heating  a  phosphate  with  carbon  and  sand.  The 
phosphorus  is  reduced  and  volatilized  while  the  remainder  of  the 
charge  melts  to  a  slag.  As  the  charge  must  be  heated  in  the 
absence  of  air,  the  electric  furnace  is  particularly  suitable  for  its 
treatment.  Both  arc  and  resistance  methods  of  heating  are  em- 
ployed. 

Carbon  Bisulphide. — This  is  another  electric  furnace  product, 
and  is  made  by  heating  carbon  and  sulphur.  The  electric  current 
passes  through  a  mass  of  broken  carbon,  which  becomes  strongly 
heated.  The  sulphur,  melted  by  the  waste  heat  of  the  furnace, 
flows  down  into  the  hot  portion  of  the  furnace,  where  it  reacts 
with  the  carbon,  forming  carbon  bisulphide,  which  passes  off  as 
a  gas,  and  is  condensed  outside  the  furnace.  The  production  of 
phosphorus  and  carbon  bisulphide  in  the  electric  furnace  is  de- 
scribed in  Wright's  "Electric  Furnaces  and  their  Industrial  Ap- 
plication,'' and  in  the  volumes  of  the  Electrochemical  Industry. 

V. — Electrolytic  Processes. 

Electrolysis. — The  use  of  a  "direct"  current  for  dividing  a 
chemical  compound  into  two  component  parts  has  already  been 
mentioned,  see  "Electrolytic  Furnaces,"  p.  30,  but  a  few  words 
may  be  added  here.  When  a  direct  or  continuous  current  flows 
through  a  fused  salt,  or  a  solution  of  a  salt  in  water,  the  salt, 
or  the  water,  is  broken  up  by  the  current  into  two  parts.  One  of 
these  parts  is  hydrogen,  or  a  metal,  which  is  liberated  at  the 
cathode  or  electrode  through  which  the  current  leaves  the  liquid, 
while  the  remainder  of  the  salt,  or  of  the  water,  is  liberated  at  the 
anode  or  electrode  by  which  the  current  enters  the  liquid.  Thus : — 

2NaCl  (electrolysed)  =  2Na  (at  cathode)  +  C\2  (at  anode).  That 
is  to  say,  when  fused  common  salt  is  electrolysed,  sodium  is  set' 
free  at  the  cathode  and  chlorine  at  the  anode. 


ELECTROLYTIC    PROCESSES.  175 

CuSO4  (electrolysed  in  aqueous  solution)  =  Cu  (at  cathode)  -+- 
SO4  (at  anode).  That  is  to  say,  the  electrolysis  of  a  solution 
of  copper  sulphate  in  water  liberates  copper  at  the  cathode  while 
804  is  set  free  at  the  anode.  The  final  result  of  the  operation 
will  depend,  however,  upon  the  nature  of  the  anode.  If  this  is 
of  platinum,  or  carbon,  and  is  not  attacked  by  the  SC>4,  the  latter 
will  react  with  the  water  of  the  solution  and  will  form  sulphuric 
acid  and  oxygen,  thus:  — 


and  the  end  products  of  the  electrolysis  will  be  copper  at  the 
cathode  and  oxygen  at  the  anode.  If,  however,  the  anode  were 
made  of  copper  or  some  other  metal  that  would  be  acted  on  by 
the  SO4,  this  reaction  would  take  place  :  — 


The  copper  sulphate  solution  would  thus  be  regenerated,  no  oxygen 
would  be  liberated,  and  the  only  result  of  the  operation  would  be  a 
transfer  of  copper  from  the  anode  to  the  cathode. 

The  latter  case  is  exemplified  in  the  electrolytic  refining  of 
copper,  the  anode  consisting  of  impure  copper,  which  constantly 
dissolves  under  the  action  of  the  current,  while  pure  copper  is  de- 
posited on  the  cathode.  When  it  is  desired  to  extract  a  metal 
from  the  fused  salt  or  solution  in  which  it  is  contained,  the  anode 
should,  if  possible,  be  insoluble  in  whatever  is  set  free  at  its 
surface  ;  or,  if  this  is  impossible,  it  should  be  inexpensive,  as  it 
will  be  dissolved  in  proportion  as  the  other  metal  is  recovered. 

In  the  equation  given  above  for  the  electrolysis  of  fused 
common  salt,  chlorine  and  sodium  are  the  end  products.  An 
aqueous  solution  could  not  be  used  for  the  production  of  sodium, 
as  the  water  would  react  with  the  sodium,  forming  caustic  soda 
and  hydrogen. 

In  the  electrolysis  of  a  fused  mixture  of  two  salts  or  of  a 
solution  of  a  salt  in  water,  the  current  breaks  up  the  compound 
which  is  the  least  stable  ;  thus  in  a  solution  of  copper  sulphate 
in  water,  the  current  separates  the  copper  sulphate  into  its  com- 
ponents, and  not  the  water;  but  in  a  solution  of  aluminium  sul- 
phate, the  water  and  not  the  aluminium  salt  is  decomposed.  It  is 
necessary,  therefore,  to  employ  a  solvent  that  is  more  stable  than 
the  salt  it  is  desired  to  decompose,  or,  failing  this,  to  use  the 
pure  salt  in  a  state  of  fusion.  This  is  why  the  extraction  of 
aluminium  from  its  ore  is  carried  out  in  a  fused  mixture  of 
fluorides  instead  of  in  an  aqueous  solution. 


176  THE     ELECTRIC     FURNACE. 

In  the  electroylsis  of  solutions  a  definite  amount  of  electricity 
in  passing  through  the  solution  will  always  produce  a  definite 
amount  of  decomposition.  This  amount  is  always  the  same  for 
the  same  solution,  and  in  different  solutions  chemically  equivalent 
amounts  of  decomposition  are  effected.  A  current  of  one  ampere 
flowing  through  acidulated  water  for  one  second  will  liberate 
0.0104  milligrams  of  hydrogen,  and  in  any  other  solution  the 
weight  of  the  metal  liberated  will  be  0.0104  milligrams,  multiplied 
by  the  atomic  weight  of  the  metal  and  divided  by  the  valency  of 
the  metal  in  the  particular  solution.  Thus,  the  amount  of  the 
monovalent  metal  sodium  that  would  be  set  free  per  second  would 
be  0.0104  mg.  X23,  the  atomic  weight  of  sodium,  or  0.239  mg.  ; 
while  the  weight  of  copper  deposited  would  be  0.0104  mg.  x63-2, 
the  atomic  weight  of  copper,  or  0.657  mg.  in  cuprous  salts,  such 
as  Cii2Cl2,  in  which  copper  is  monovalent,  while  in  the  more 
usual  ctipric  salts,  such  as  CuSO4,  in  which  the  metal  is  divalent, 
only  half  that  amount  would  be  deposited  by  the  current.  The 
amount  of  metal  actually  obtained  as  the  result  of  electrolysis  vs 
frequently  less  than  the  calculated  weight  on  account  of 
secondary  reactions,  such  as  the  metal  redissolving  in  the 
electrolyte,  hydrogen  being  liberated  instead  of  the  metal,  leak- 
age of  the  current,  etc.,  and  the  ratio  of  the  metal  actually  de- 
posited to  the  theoretical  quantity  is  known  as  the  current 
efficiency,  as  it  shows  what  proportion  of  the  current  is  effective 
in  liberating  the  metal. 

The  electrical  energy  necessary  to  produce  a  definite  weight 
of  a  metal,  by  the  electrolysis  of  a  chemical  compound  of  the 
metal,  depends  not  only  on  the  number  of  ampere  hours  needed 
to  liberate  the  weight  of  metal,  but  also  on  'the  voltage  of  the 
operation  ;  that  is  on  the  electrical  pressure  needed  to  drive  the 
electric  current  through  the  electrolyte  so  as  to  produce  the  de- 
composition. Each  solution  has  a  definite  electrical  pressure 
which  must  be  exceeded  before  electrolysis  will  take  place,  and 
the  working-  voltage  must  be  decidedly  above  the  minimum  in 
order  to  drive  a  rapid  current  of  electricity  through  the  solution. 
The  passage  of  the  current  also  produces  heat,  the  amount  being 
proportional  to  the  square  of  the  current  and  to  the  resistance  of 
the  electrolytic  cell,  while,  as  has  been  noted,  the  amount  of 
metal  deposited  is  proportional  to  the  current  alone.  For  a  given 
amount  of  chemical  work  accomplished,  the  heat  generated  will 
be  less  if  the  current  is  small,  than  if  a  large  current  is  employed, 
and  therefore  the  efficiency  of  the  operation  will  be  greater  with 


ELECTROLYTIC    PROCESSES.  177 

the  smaller  current.  In  electrolysis  at  furnace  temperatures, 
however,  it  is  often  convenient  to  heat  the  electrolyte  electrically 
instead  of  by  the  external  application  of  fuel  heat,  and  in  such 
cases  the  production  of  heat  by  the  current  cannot  be  regarded  as 
waste. 

The  nature  of  the  anode  has  a  great  effect  upon  the  voltage 
needed  for  electrolysis.  Thus,  electrolysing  a  solution  of  copper 
sulphate  with  an  anode  that  does  not  dissolve,  copper  and  oxygen 
would  be  liberated,  the  electric  current  would  have  to  do  the 
work  of  separating  these  elements,  and  a  pressure  of  more  than 
one  volt  would  be  needed ;  but  if  the  anode  were  made  of  copper, 
this  would  dissolve  as  fast  as  the  copper  deposited  on  the  cathode, 
no  chemical  work  would  be  done,  and  the  smallest  voltage  would 
suffice  to  produce  electrolysis.  It  is  possible  to  calculate,  from 
available  data,  the  amount  of  energy  needed  to  separate  a  definite 
weight  of  a  compound  into  its  elements,  and  the  relation  of  this 
to  the  electrical  energy  actually  required  to  produce  this  de- 
composition is  the  energy  efficiency  of  the  process. 

When  an  anhydrous  salt  or  mixture  of  salts  is  used  as  an 
electrolyte  it  must  be  heated,  usually  to  a  red  heat,  to  render  it 
fluid,  and  its  electrolysis  may  be  classed  as  a  furnace  operation. 
Some  examples  of  these  electrolytic  furnace  processes  will  now 
be  given. 

The  Acker  Process  for  Caustic  Soda  and  Chlorine. — In  this 
process  fused  common  salt  or  sodium  chloride  is  electrolysed, 
using  carbon  anodes  by  which  the  current  enters  the  liquid,  and 
molten  lead  for  the  cathode  by  which  the  current  leaves.  The 
salt  is  broken  up  into  chlorine,  which  is  liberated  at  the  anode 
and  is  led  away  and  used  for  making  bleaching  powder,  and 
sodium,  which  is  liberated  at  the  cathode  and  alloys  with  the  lead. 
The  lead  containing  the  sodium  is  then  treated  with  steam,  which 
combines  with  the  sodium  to  form  caustic  soda. 

The  following  reactions  take  place  : — 

2\aCl  (electrolysed)  =  C\2  (liberated  at  the  anode)  +  2Na 
(alloying  with  the  lead  cathode). 

2X3  (alloyed  with  the  lead)  +  2H2O  (the  jet  of  steam)  = 
2\aOH  +  H2. 

The  ingenious  arrangement  by  which  this  is  accomplished  is 
illustrated  in  Fig.  49.  The  apparatus  consists  of  an  irregular 
shaped  cast  iron  vessel,  about  5  feet  long,  which  is  divided  into 
three  compartments,  A,  B,  and  C,  with  the  connecting  channel, 
R.  The  larger  compartment,  A,  contains  melted  salt,  S,  resting 


17.8 


THE    ELECTRIC    FURNACE. 


on  a  thin  layer  of  molten  lead  which  is  caused  to  circulate  as 
shown  by  the  arrows.  Four  electrodes,  E,  of  graphitized  carbon 
are  immersed  in  the  fused  salt  and  form  the  anode  of  the 
electrolytic  cell,  being  connected  to  the  positive  cable  from  a 
dynamo.  The  iron  tank  is  connected  at  the  point  H  to  the 
negative  cable,  thus  making  the  molten  lead,  the  cathode.  The 
electric  current  passes  from  the  carbon  electrodes  through  the 
melted  salt  to  the  fused  lead  on  which  the  salt  rests.  In  passing 
through  the  salt,  chlorine  is  liberated  at  the  carbon  electrodes 
and  escapes,  being  drawn  away  by  a  fan,  while  the  sodium  is 
liberated  at  the  surface  of  the  lead  and  alloys  with  it.  In  the  small 
compartment,  B,  a  jet  of  steam  introduced  by  the  pipe,  F,  serves 
to  blow  the  lead  up  the  vertical  pipe,  P,  and  over  into  the  third 
compartment,  C,  from  which  the  lead  returns  by  the  passage,  R, 
to  the  first  compartment.  The  lead  entering  B  is  charged  with 
sodium,  and  when  it  meets  the  steam  in  the  pipe,  P,  the  sodium 


Fig.  49. — Acker's  Caustic  Soda  Furnace. 

combines  with  the  steam,  forming  anhydrous  caustic  soda,  which 
floats  on  the  lead  in  C  and  overflows  by  the  spout,  D,  and 
hydrogen,  which  escapes  at  D  and  burns.  The  compartment  A 
is  lined,  above  the  level  of  the  lead,  with  magnesite  bricks,  M, 
and  the  cover  is  formed  of  fire-brick  tiles,  T.  The  salt  to  be 
used  in  the  process  is  warmed  on  the  top  of  the  furnace  and  then 
introduced  through  charging  holes  in  the  roof.  Each  anode 
consists  of  a  block  of  graphitized  carbon  14  inches  long,  7/2 
inches  wide,  and  3  inches  thick,  which  is  supported  by  two  five- 
inch  carbon  rods  passing  through  the  top  of  the  furnace.  The 
carbon  blocks  are  lowered  until  within  3/^-inch  of  the  molten 
lead.  The  current  used  is  8,200  amperes,  the  voltage  of  each 
furnace  or  pot  being  only  6  or  7.  From  40  to  45  pots  are  used 
at  once,  being  connected  in  series,  so  that  the  same  current  passes 
through  them  all,  and  the  total  voltage  necessary  is  275;  about 


ELECTROLYTIC    PROCESSES.  179 

3,000  horse-power  being  supplied  at  the  generating  station,  which 
is  1,500  feet  away.  The  current  density  at  the  anodes  is  about 
2,750  amperes  per  square  foot,  and  this  is  sufficient  to  keep  the 
salt  at  a  temperature  of  85O°C.,  which  is  a  bright  red  heat,  and 
75°C.  above  the  melting  point  of  the  salt,  while  it  is  far  above 
the  melting  point  of  lead.  The  cast-iron  vessel  which  forms  the 
furnace  is  set  in  brick-work  which  reduces  the  loss  of  heat  by 
radiation  and  conduction.  The  output  of  each  furnace  is  25 
pounds  of  caustic  per  hour,  which  is  93  per  cent,  of  the  amount 
which  should  theoretically  be  produced  by  the  current,  but  the 
voltage  is  considerably  higher  than  is  required  by  theory,  as 
nearly  half  of  the  energy  of  the  current  is  needed  to  keep  the 
furnace  at  the  high  temperature  of  fused  salt.  The  caustic  soda 
in  C  is  fused  and  practically  anhydrous,  so  that  it  is  ready  for 
market  without  any  boiling  down,  such  as  is  required  when 
aqueous  solutions  are  used  for  electrolysis.  The  Acker  process 
has  been  described  by  C.  E.  Acker  in  the  Transactions  of  the 
American  Electrochemical  Society,  vol.  i.,  1902,  and  by  Prof. 
Richards,  Electrochemical  Industry,  vol.  i.,  1902,  p.  54.  The 
works  of  the  Acker  Process  Company  at  Niagara  Falls  was  burned 
down  early  in  the  year  1907,  causing  a  loss  of  $800,000. 

The  Castner  Sodium  Process. — This  is  the  standard  method 
of  making  that  metal,  and  no  less  than  3,500  tons  per  annum  are 
now  made  in  this  manner.  In  this  process,  fused  anhydrous 
caustic  soda  is  electrolysed,  using  nickel  for  the  anode,  and  car- 
bon, or  some  metal  such  as  iron,  for  the  cathode.  The  products 
of  the  operation  are  sodium  and  hydrogen  at  the  cathode,  and 
oxygen  at  the  anode,  all  in  equal  atomic  proportions. 

The  following  reactions  probably  take  place : — 

2XaOH    (electrolysed)  =  2Na   (at  cathode) +  2HO  (at   anode). 

4HO  (at  anode)  =  2H2O  + O2. 

2H2O  (electrolysed)  =  2 Hz   (at  cathode)  +  Oz  (at  anode). 

Or,  put  into  one  equation  : — 

2\aOH  (electrolysed)  =  [Na2  +  H2]  (at  cathode) +  O2  (at  an- 
ode). 

As  the  sodium  is  lighter  than  the  fused  caustic,  it  floats  to 
the  top,  and  great  difficulty  is  experienced  in  preventing  it  from 
burning  in  the  air  or  in  the  oxygen  liberated  at  the  anode,  which 
also  rises  to  the  surface.  In  the  Castner  apparatus,  Fig.  50,  this 
is  accomplished  by  the  metal  cylinder  E,  from  the  lower  edge  of 
which  a  cylinder  of  nickel  gauze  is  continued  down  between  the 
nickel  anode  C  and  the  cathode  D.  The  sodium  rises  within  this 


i8o 


THE    ELECTRIC    FURNACE. 


cylinder  and  collects  at  F,  from  which  it  may  be  ladled,  or  may 
overflow  through  a  spout,  while  the  oxygen  rises  outside  the  gauze 
cylinder,  and  is,  therefore,  unable  to  attack  the  sodium.  The 
hydrogen  rises  with  the  sodium  inside  the  cylinder  and  escapes 
through  the  holes  in  the  cover.  The  use  of  the  gauze  cylinder 
allows  the  anode  and  cathode  to  be  brought  very  close  to  each 
other,  being  only  one  inch  apart,  without  danger  of  the  sodium 
meeting  the  oxygen,  and  in  this  way  the  resistance  of  the  ap- 
paratus is  kept  low,  and  a  high  electrical  efficiency  can  be  ob- 
tained. 


Fig.  50. — Castner's  Sodium  Furnace. 

The  apparatus  consists  of  a  cast-iron  pot  A,  set  in  brick- 
work, B,  and  heated  if  necessary  by  a  ring  of  gas  burners,  H,  to 
a  temperature  very  little  above  the  melting  point  of  the  caustic 
soda.  The  cathode,  D,  is  supported  in  position  and  insulated 
from  the  iron  pot  by  means  of  the  tube,  G,  which,  being  closed 
at  the  bottom  by  a  ring  of  insulating  material,  such  as  porcelain, 
is  filled  with  the  fused  caustic  soda,  which  is  then  allowed  to 
solidify.  The  tube  is  kept  a  little  cooler  than  the  rest  of  the 
apparatus,  and  the  caustic  in  G,  therefore,  remains  solid,  and 
supports  and  insulates  the  cathode.  It  is  very  important  that  the 


ELECTROLYTIC  PROCESSES.  l8l 

fused  caustic  should  not  be  heated  far  above  its  melting  point, 
because  the  sodium  would  then  rapidly  redissolve  in  it.  The 
caustic  melts  at  about  3oo°C.,  and  should  be  kept  not  more  than 
10°  above  this;  90  per  cent,  of  the  theoretical  quantity  of  sodium 
being  then  obtained.  If  heated  20°  above  its  melting  point  no 
sodium  would  be  produced,  as  it  would  dissolve  as  rapidly  as  it 
formed.  A  pot  18  inches  in  diameter  and  two  feet  deep  will  hold 
250  pounds  of  melted  caustic,  and  takes  a  current  of  1,200  am- 
peres at  five  volts.  The  current  density  is  2,000  amperes  per 
square  foot  at  the  cathode  and  1,500  at  the  anode.  At  the 
Niagara  Electrochemical  Company's  plant  in  1902*  there  were 
120  such  pots,  employing,  in  all,  1,000  horse-power,  and  produc- 
ing about  50  pounds  each  per  day,  or  6,000  pounds  for  the  whole 
plant.  The  consumption  of  power  was  about  four  horse-power 
hours  per  pound  of  sodium. 

Of  the  total  annual  production  of  sodium,  about  1,500  tons 
are  used  for  cyanide  making,  1,500  tons  for  making  sodium  per- 
oxide, and  500  tons  are  sold  in  the  metallic  state. 

The  Ashcroft  Sodium  Process. t — This  is  an  attempt  to  pro- 
duce sodium  from  common  salt  instead  of  from  the  more  ex- 
pensive caustic  soda.  Common  salt  has  so  high  a  fusing 
temperature  that  it  cannot  be  electrolysed  directly  for  the  metal 
sodium,  as  this  would  be  volatilized.  In  the  Acker  process  sodium 
is  produced,  but  only  as  an  alloy  with  molten  lead,  from  which 
it  is  recovered  as  caustic  soda.  The  Ashcroft  process,  illustrated 
in  Fig.  51,  consists  in  electrolysing  fused  salt  in  a  tank,  A,  using 
lead  as  the  cathode  to  retain  the  resulting  sodium,  and  then  carry- 
ing the  sodium  lead  alloy  to  a  second  tank,  B,  where  it  becomes 
the  anode,  in  a  bath  of  fused  caustic  soda  kept  just  above 
its  melting  point.  In  this  tank  metallic  sodium  is  liberated  at 
the  cathode,  C,  and  floating  upward  is  caught  within  the  hood 
D,  and  overflows  through  the  pipe  E. 

The  reactions  that  take  place  can  be  made  clear  by  the  fol- 
lowing equations : — 
In  A — 2NaCl    (electrolysed)  =  C\2    (liberated  at   the   anode)  -f  2Na 

(dissolving  in  the  lead  cathode) (i) 

In  B— NaOH    (electrolysed)  =  HO    (at   anode)  +  Na    (liberated    at 

the   cathode)          (2) 

Na  (in  lead  alloy)   -f-HO  =  NaOH       (3) 

*Richards,   Electrcchem.    Ind.,   vol.    i.,    1902,   p.    15. 

•f-Ashcroft,   Trans.   Am.    Electrcchem.    Soc.,   vol.    ix.,   1906,   p.    123;   Electrochem.    and 
Met.    Ind.,   vol.    iv.,   1906,   p.   218. 

13 


182 


THE     ELECTRIC     FURNACE. 


In  A,  with  an  insoluble  anode,  the  salt,  which  forms  the 
electrolyte,  is  broken  up  into  chlorine  and  sodium.  In  B,  the 
caustic  soda  electrolyte  is  re-formed  by  reaction  (3)  as  fast  as  it 
is  destroyed  by  reaction  (2). 


Fig.  51. — Ashcroft's  Sodium  Furnace. 


The  products  of  the  first  tank  are  chlorine,  which  is  piped 
away  and  utilized,  and  sodium  as  an  alloy  writh  lead  ;  while  com- 
mon salt  is  consumed.  The  second  tank  yields  sodium  only, 
which  it  takes  from  the  lead  alloy.  The  fused  caustic,  which 
serves  as  electrolyte,  is  not  destroyed,  but  merely  serves  as  a 
carrier  for  the  sodium.  The  electric  current  will  liberate 
twice  as  much  sodium  as  in  the  Castner  process,  because  only 
sodium  is  set  free  at  the  cathode,  while  in  the  older  process  equal 
equivalents  of  sodium  and  hydrogen  were  set  free. 

As  the  tank  A  must  be  hot  enough  to  fuse  salt,  that  is  nearly 
8oo°C.,  while  the  tank  B  is  little  more  than  3oo°C.,  the  lead 
sodium  alloy  must  be  cooled  during  its  passage  from  A  to  B, 
and  the  lead  returning  from  B  to  A  must  be  reheated.  This  is 
accomplished  by  a  twin  pipe  P  of  considerable  length  connecting 
the  two  vessels,  so  that  the  alloy  flowing  from  A  to  B  gives  up 
its  heat  to  the  lead  flowing  from  B  to  A.  The  pipe  is  folded  on 
itself  for  compactness,  only  a  part  being  shown  in  the  drawing. 
The  method  of  producing  a  continuous  circulation  of  the  lead  is 


ELECTROLYTIC    PROCESSES.  183 

also  very  ingenious,  and  consists  in  producing  electro- 
magnetically,  a  rotation  of  the  lead  alloy  in  A,  and  in  providing 
a  suitable  baffle  F,  and  openings  G  and  H  in  the  end  of  the 
twin  pipe  which  enters  A,  so  that  the  rotating  alloy  is  forced  to 
pass  from  A  to  B,  circulate  in  B,  and  after  giving  up  its  sodium 
return  to  A.  The  openings  at  both  ends  of  the  twin  pipe  are  so 
arranged  that  the  richest  of  the  alloy  in  A  is  skimmed  off  and 
passes  to  B,  where  it  passes  to  the  surface,  and  so  gives  up  its 
sodium  before  returning  to  A.  The  rotation  of  the  metal  is 
shown  by  arrows  in  the  figure.  The  rotation  in  A  is  caused  by 
a  coil  of  wire  W  within  the  cast  iron  tank,  but  separated  from 
the  molten  salt  by  the  lining  of  magnesite  or  similar  material. 
The  whole  current  used  in  the  process  passes  through  this  coil 
and  produces  a  strong  magnetic  field  within  A,  the  lines  of 
magnetic  force  pointing  upward  as  shown  by  the  arrows.  After 
leaving  the  coil  the  current  passes  to  the  carbon  anode  N,  and 
then  through  the  fused  salt  to  the  molten  lead.  The  anode  being 
small  and  central,  and  the  lead  cathode  being  more  extended,  the 
direction  of  the  current  though  mainly  vertical,  will  be  partly 
horizontal,  and  so  will  cut  the  lines  of  magnetic  force.  The  re- 
sult will  be  horizontal  rotation  of  the  molten  contents  of  A,  and, 
as  has  been  explained,  this  leads  to  the  desired  circulation  of  lead 
from  A  to  B  and  back  again.  The  tanks  A  and  B  are  made  of 
cast  iron,  and  heated  externally  by  fuel  as  well  as  internally  by 
the  passage  of  the  current.  A  is  provided  with  two  openings, 
}  and  K,  one  of  which  has  a  hopper  for  charging  in  the  salt,  while 
the  other  serves  to  remove  the  chlorine.  In  B,  the  cathode  C  is 
globular  in  form,  allowing  the  sodium  which  deposits  around  it 
to  pass  easily  upwards  into  the  hood  D.  The  cathode  is  insulated 
from  the  bottom  by  a  layer  of  solidified  caustic  as  in  the  Castner 
apparatus,  and  is  hollow,  thus  allowing  of  cooling  by  air  or  other 
substances  if  the  temperature  becomes  too  high.  The  hood  D  is 
connected  to  the  iron  cover  of  B,  and  thus  with  the  sodium-lead 
anode,  so  that  there  is  no  tendency  for  sodium  to  form  on  any  part 
of  the  tank  except  the  cathode  C.  The  method  for  producing  a 
circulation  of  the  lead  does  not  sound  very  efficient,  but  it  is  stated 
to  work  well  in  a  furnace  using  some  2,000  or  3,000  amperes,  and 
the  whole  operation  is  reported  to  be  working  satisfactorily.  The 
voltage  needed  will  be  about  7  volts  in  A,  that  is,  the  same  as  in 
the  Acker  process,  and  about  2  volts  in  B,  or,  in  all,  9  volts.  The 
process  should  show  marked  economies  in  comparison  with  the 
Castner  method. 


184  THE     ELECTRIC     FURNACE. 

The  alkali  metal  potassium  strongly  resembles  sodium,  and 
is  obtained  by  electrolysis  of  its  fused  salts  in  practically  the  same 
manner.  Magnesium,  largely  used  for  flash-lights,  and  the 
alkaline  earth  metals,  barium,  calcium  and  strontium,  which  until 
recently  were  quite  rare  in  the  metallic  form,  although  lime,  the 
oxide  of  calcium,  is  so  common,  are  all  obtained  by  the  electrolysis 
of  the  fused  chlorides  of  these  metals.  Calcium  has  also  been 
obtained  by  heating  calcium  carbide  to  a  very  high  temperature 
in  the  electric  furnace.  The  carbide  dissociates,  yielding  calcium 
vapor  which  can  be  condensed.  Calcium  is  less  violent  in  its 
reactions  than  sodium  and  will  form  a  valuable  reducing  reagent 
in  certain  metallurgical  operations.  When  calcium  is  added  to 
molten  steel,  it  is  said  to  remove  very  completely  not  only  the 
oxygen,  but  also  any  nitrogen  that  may  be  contained  in  the  steel, 
forming  a  nitride  of  calcium.  Another  compound,  calcium 
hydride,  is  formed  by  heating  calcium  in  an  atmosphere  of 
hydrogen.  It  is  called  "  hydrolith  "  (hydrogen  stone),  because, 
when  placed  in  water,  it  liberates  a  large  quantity  of  hydrogen. 
The  hydrogen  is  supplied  in  part  by  the  calcium,  which  reacts 
with  water  forming  lime  and  hydrogen,  and  in  part  from  the 
hydrogen  contained  in  the  calcium  hydride,  as  shown  in  the  equa- 
tion : — 

CaH2  +  2H20  =  CaH202  +  2H2. 

One  kilogram  of  the  hydrolith  is  found  to  yield  as  much  as 
one  cubic  meter  of  hydrogen,  so  that  it  should  be  very  valuable 
for  inflating  balloons  and  for  other  purposes. 

The  Swinburne  and  Ashcroft  chlorine  smelting  process. — This 
is  a  method  for  the  treatment  of  mixed  sulphide  ores  such  as  those 
of  zinc  and  lead.  Although  largely  a  chemical  process,  the  final 
stage  is  carried  out  in  an  electric  furnace,  and  a  short  account 
may,  therefore,  be  given  here. 

The  ore,  consisting  of  sulphides  of  lead,  zinc,  iron,  and 
manganese,  with  some  silver,  is  decomposed  by  the  action  of  dry 
chlorine  at  a  temperature  of  6oo°C. ,  or  7oo°C. ,  in  a  special  vessel 
called  a  transformer,  forming  a  fused  mixture  of  chlorides  of  the 
metals.  The  sulphur  comes  off  in  the  free  state,  and  can  be 
condensed  and  saved,  whilst  the  earthy  mattter  or  gangue,  from 
the  ore,  remains  suspended  in  the  fused  chlorides.  Enough  heat 
is  produced  by  the  reaction  to  keep  the  transformer  at  the  right 
temperature,  which  can  be  regulated  by  passing  the  chlorine  more 
or  less  rapidly.  When  the  vessel  is  full  of  chlorides  they  are 
tapped  out,  leaving  enough  behind  to  serve  as  a  molten  bath  into 


ELECTROLYTIC    PROCESSES.  185 

which  more  ore  can  be  charged,  and  through  which  the  chlorine 
can  be  passed.  The  molten  chlorides  are  treated  with  molten 
lead,  which  serves  to  remove  the  silver,  and  with  zinc  to  remove 
the  lead.  The  remaining  chlorides  are  dissolved  in  water,  separ- 
ated from  the  gangue  by  filtration,  and  the  iron  and  manganese 
precipitated  chemically  by  the  addition  of  chlorine  and  zinc  oxide, 
leaving  a  solution  of  zinc  chloride  only.  This  solution  is  evapor- 
ated, and  then  fused  and  electrolysed  in  a  furnace  shown  in  out- 
line in  Fig.  19,  p.  30.  The  products  are  molten  zinc,  which  is 
tapped  off  at  intervals,  and  chlorine,  which  is  compressed  and 
used  again  for  the  treatment  of  fresh  quantities  of  ore.  The 
process  is  one  of  great  interest,  and  is  applicable  to  very  many 
complex  ores  which  are  difficult  to  treat  by  other  methods.  It 
is  self-contained,  and  does  not  require  any  expensive  reagents,  as 
the  chlorine  for  the  transformer  is  produced  in  the  electrolysis  of 
the  zinc  chloride,  but  the  operations  are  somewhat  complicated, 
and  would  need  very  careful  attention.  At  present  the  only  com- 
merical  installation  is  at  a  plant  of  the  Castner-Kellner  Co. ,  which 
has  a  supply  of  chlorine  from  other  processes,  and  uses  it  for  the 
treatment  of  complex  ores  as  described  above,  but  omits  the 
final  electrolysis,  obtaining  the  zinc  in  the  form  of  chloride.  Ac- 
counts of  this  process  can  be  found  in  the  "Electrochemical  In- 
dustry," vol.  i.,  p.  412;  vol.  ii.,  p.  404;  vol.  iii.,  p.  63,  the 
transactions  of  the  Institution  of  Mining  and  Metallurgy  for  1901, 
and  the  Mineral  Industry,  vols.  x.  and  xi. 

Aluminium. — This  is  the  most  important  metal  that  is  pro- 
duced solely  in  the  electric  furnace.  Originally  it  was  obtained  by 
complicated  chemical  methods  involving  the  use  of  metallic  sodium 
as  a  reducing  agent,  but  the  electrical  method,  described  on  page 
7,  entirely  supplanted  the  older  processes.  The  common  metals — 
iron,  copper,  lead,  tin,  zinc,  etc. — occur  in  their  ores  as  oxides, 
or  can  easily  be  converted  into  oxides  by  a  roasting  operation, 
and  these  oxides  are  readily  reduced  to  the  metallic  state  by  the 
action  of  carbon  in  an  ordinary  furnace,  because,  at  such  tempera- 
tures, oxygen  has  a  greater  affinity  for  carbon  than  it  has  for  the 
metal.  Other  metals,  however,  such  as  aluminium,  calcium, 
and  sodium,  have  a  greater  affinity  for  oxygen  than  those  already 
mentioned,  and  it  is  very  difficult,  and  in  some  cases  impossible, 
to  reduce  the  oxides  of  these  metals  by  means  of  carbon  at  ordin- 
ary furnace  temperatures.  With  the  aid  of  electricity,  however, 
any  metal  can  be  reduced,  either  by  heating  the  oxide  to  a  very 
high  temperature,  at  which  the  affinity  between  the  metal  and 


1 86 


THE     ELECTRIC     FURNACE. 


oxygen  is  lessened,  so  that  the  latter  can  be  removed  by  means 
of  carbon,  or  by  dissolving  the  oxide  or  other  ore  of  the  metal 
in  a  suitable  solvent,  and  applying  an  electrical  force  to  tear  the 
compound  into  two  parts  by  electrolysis,  thus  liberating  the  metal. 
Aluminium,  calcium,  and  other  metals  can  be  reduced  by  carbon 
at  the  high  temperature  of  the  electric  furnace,  but  immediately 
combine  with  a  further  quantity  of  carbon,  forming  carbides. 
It  is,  therefore,  necessary,  when  the  pure  metal  is  desired,  to  em- 
ploy electrolysis  instead  of  the  direct  reduction  with  carbon. 

Aluminium  has  been  termed  "Silver  from  Clay"  as  it  forms 
some  15  or  20  per  cent,  of  ordinary  clay,  but  the  expense  of  ex- 
tracting aluminium  from  clay  would  be  so  great  that  the  richer 


Fig.  52. — Aluminium  Furnace. 

ore,  bauxite,  is  always  employed  as  a  source  of  this  metal. 
Bauxite  consists  of  alumina,  the  oxide  of  aluminium,  combined 
with  some  water  and  associated  with  silica,  oxide  of  iron,  etc.  If 
the  natural  bauxite  were  merely  calcined  to  remove  the  water 
and  then  electrolysed  in  the  electric  furnace,  the  iron  and  silicon 
would  be  reduced  more  readily  than  the  aluminium.  The  result- 
ing metal  would  therefore  be  impure  and  would  be  almost  useless 
for  most  of  the  purposes  to  which  aluminium  is  applied,  though 
an  impure  metal,  obtained  in  this  way,  would  serve  for  the  pro- 
duction of  high  temperatures  by  Dr.  Goldschmidt's  Thermit 
process.  For  the  production  of  the  pure  metal  the  bauxite  must 
be  purified  before  being  introduced  into  the  electrolytic  furnace. 


ELECTROLYTIC    PROCESSES.  187 

One  method  of  effecting  this  was  to  digest  the  calcined  bauxite 
in  a  soluticn  of  caustic  soda.  This  dissolved  the  alumina  which 
was  subsequently  precipitated  from  the  solution.  A  more  re- 
cent process,  that  of  Hall,  consists  in  mixing  the  calcined  bauxite 
with  a  sufficient  proportion  of  carbon  or  aluminium  to  reduce  the 
whole  of  the  impurities  to  the  metallic  state.  The  mixture  is 
then  charged  into  a  carbon  lined  electric  furnace  and  melted. 
The  iron,  silicon  and  other  impurities  are  reduced  to  the  metallic 
state  and  collect  at  the  bottom  of  the  melted  mass,  leaving  a  pure 
fused  alumina  suitable  for  use  in  the  electrolytic  furnace. 

The  production  of  aluminium  from  alumina  is  effected  by 
electrolysis  as  described  in  outline  on  page  7,  Fig.  52*  represents 
cliagrammatically  a  furnace  used  by  the  Pittsburg  Reduction  Com- 
pany. The  furnace  consists  of  an  iron  casing,  B,  thickly  lined 
with  carbon,  D,  and  containing  the  fused  electrolyte,  C,  and 
aluminium,  A.  A  number  of  electrodes  of  specially  pure  carbon 
E  E,  form  the  anode,  while  the  carbon  lining,  D,  and  aluminium, 
A,  form  the  cathode  of  the  furnace.  The  carbon  lining  is  very 
thick,  thus  reducing  the  loss  of  heat,  and  is  provided  with  a  sump 
for  holding  the  aluminium  when  it  is  formed.  A  tapping  hole 
and  spout,  leading  from  this  sump,  are  also  provided  though 
not  shown  in  the  figure.  The  electrolyte  consists  of  alumina  dis- 
solved in  the  fluorides  of  sodium,  aluminium,  and  possibly  calcium. 
The  fluorides  are  not  decomposed  but  merely  serve  as  a  solvent 
for  the  alumina.  Electrolysis  of  the  alumina  yields  aluminium  at 
the  cathode  and  oxygen  at  the  anode.  The  oxygen  combines 
with  the  carbon  of  the  anodes  as  shown  in  this  equation  :  — 


Only  a  small  proportion  of  alumina  can  be  dissolved  by  the 
fluorides,  without  unduly  raising  the  temperature  of  the  furnace, 
but  a  quantity  of  alumina  is  placed  on  the  top  of  the  electrolyte 
and  stirred  in  from  time  to  time  as  required.  It  is  desirable 
that  the  furnace  should  be  worked  at  a  low  temperature  and  with 
?  low  current  density,  as  a  high  temperature  leads  to  the  re- 
solution of  the  deposited  metal  in  the  electrolyte,  and  a  high  cur- 
rent density  causes  the  fluorides  to  be  decomposed  liberating 
sodium  and  fluorine.  The  melting  temperature  of  the  most 
fusible  mixture  of  cryolite,  the  natural  fluoride  of  aluminium  and 
sodium,  and  alumina  has  been  found  to  be  9i5°C.  ,t  but  it  has 


*From    a    drawing    by    Prof.    J.    VV.    Richards    in    the    Journal    of    the    Franklin    In- 
stitute,  May,   1896. 

•f-F.   R.    Pyne,   Trans.    Amer.   Electrochem.    Soc.,  vol.    x.,  p.  63. 


1 88  THE     ELECTRIC     FURNACE. 

been   stated     that   in   recent  practice    the   aluminium   furnace     is 
worked  at  75o°C.  or  8oo°C. 

The  aluminium  industry  is  growing  rapidly  at  the  present 
time,  and  an  extended  use  of  the  metal  will  no  doubt  follow  the 
larger  supply.  Prof.  Richards*  gives  the  total  production  of 
aluminium  in  1906  as  not  far  short  of  19,000  metric  tons,  valued 
at  $12,500,000,  and  says  that  the  output  in  1907  will  probably 
be  twice  as  great  as  in  1906,  and  that  in  1908  the  production  of 
aluminium  will  probably  be  twice  as  great  as  in  1907. 


*J.    W.    Richards,    Engineering    and    Mining    Journal,    vol.    Ixxxiii,    p.    1083,    and    the 
Mineral    Industry,    vol.    xv. 


FUTURE    DEVELOPMENTS.  189 

CHAPTER  VII. 
Future  Developments  of  the  Electric  Furnace. 

In  this  concluding  chapter,  an  attempt  may  be  made  to 
indicate  in  what  directions  future  developments  of  the  electric 
furnace  may  be  expected,  and  to  what  extent  this  development  is 
likely  to  proceed.  Such  an  attempt  can  hardly  fail  to  prove 
incorrect,  however,  on  account  of  the  great  changes  that  take 
place  in  the  economic  conditions  of  the  world,  as  well  as  on  ac- 
count of  the  discoveries  and  improvements  which  are  made  with 
increasing  frequency. 

The  following  questions  may  be  asked  :— 

1.  How  far  will  the  electric  current  replace  fuel  in  furnaces 
for  the  smelting  and  refining  of  metals? 

2.  What  untouched  fields  of  usefulness  are  waiting  for  the 
electric  furnace? 

3.  What  limits  are  there  to  the  commercial  development  of 
the  electric  furnace? 

Electric  furnace  operations  may  be  roughly  divided  into  two 
classes,  first,  those  which  can  scarcely  be  effected  in  any  other 
way,  and  in  which  electrical  heating  must  always  hold  the  field, 
such  as  the  production  of  calcium  carbide,  carborundum,  and 
aluminium.  Second,  those  in  which  either  fuel  or  electrical  heat 
may  be  used  with  a  fair  measure  of  efficiency,  and  in  which  the 
price  of  the  two  sources  of  heat  must  be  compared, 
in  addition  to  the  efficiency  of  each,  before  deciding  which 
to  employ. 

The  relative  prices  of  coal  and  electrical  energy,  and  the 
amount  of  electrical  power  that  will  be  available,  are  considera- 
tions of  the  first  importance  in  determining  the  future  of  the 
electric  furnace. 

Until  a  few  years  ago  the  electric  current  was  a  wonderful 
and  expensive  commodity,  and  the  idea  of  using  it  for  heating  on 
a  commercial  scale  was  preposterous.  About  13  tons  of  coal 
were  needed  to  produce  one  electrical  horse-power  for  a  year, 
and  this  electrical  energy,  would  furnish  less  heat  than  one  ton 
of  the  original  coal.  Such  a  method  of  using  coal  was  evidently 
extremely  wasteful.  The  greater  efficiency  of  electrical  heating 
somewhat  reduces  this  difference,  and  together  with  the  smaller 
cost  of  water-power  has  made  it  cheaper  in  some  cases  to  use 
"white  coal"  instead  of  black,  in  the  furnace. 


IQO  THE     ELECTRIC     FURNACE. 

In  comparing-  the  supplies  and  prices  of  coal  and  electrical 
energy,  it  should  be  remembered  that  one  ton  of  good  coal  pro- 
duces as  much  heat  as  1^3  horse-power  years  of  electrical  energy, 
but  that  the  efficiency  of  the  electrical  furnace  is  from  2  to  30 
times  as  great  as  the  efficiency  of  ordinary  metallurgical  furnaces, 
sc,  that  an  electrical  horse-power  year  will  produce  as  much 
effective  heat  as  several  tons  of  coal.  The  figures  for  different 
operations  are  given  in  Chapter  III.,  page  34. 

The  world's  production  of  coal  at  the  present  time  is  about 
1,000  million  tons  a  year,  and  is  steadily  increasing.  The  electric 
furnace  draws  its  energy  mainly  from  water-powers.  The 
water-powers  of  the  world  that  have  already  been  utilized  are 
very  small  in  comparison  with  the  present  coal  output,  having  in 
all  only  about  i  per  cent,  of  the  heating  power  of  the  latter. 

In  view  of  the  fact  that  coal  mining  is  a  long-established 
industry,  while  the  electrification  of  water-powers  is  only  of 
recent  growth,  it  is  reasonable  to  suppose  that  the  latter  will  in- 
crease more  quickly  in  proportion  than  the  former.  In  both  cases 
there  are  limits,  however;  the  coal  mines  will  ultimately  all  be 
discovered  and  worked  out  to  a  depth  at  which  the  cost  become? 
almost  prohibitory,  while  on  the  other  hand  the  water-powers  will 
all  be  developed,  leaving  only  those  that  are  too  expensive  to 
utilize.  When  these  limits  are  reached  the  coal  supply  will  have 
sunk  to  a  small  proportion  of  the  amount  needed  for  heating  and 
power,  but  the  water-powers  will  continue  to  give  a  steady  supply 
of  power  for  all  time  with  only  maintenance  and  interest  charges. 
The  exhaustion  of  coal  supplies  may  not  be  reached  for 
hundreds  or  thousands  of  years,  but  if  the  development  of  the 
mines  proceeds,  as  at  present,  at  increasing  rates  like  compound 
interest,  their  practical  depletion  may  be  less  distant  than  now  ap- 
pears probable.  In  any  case  it  seems  likely  that  as  coal  can  only 
be  used  once,  while  water-powers  are  not  deteriorated  by  use, 
the  latter  may  be  expected  ultimately  to  largely  replace  the  former 
for  motive  power  and  to  some  extent  for  furnace  work. 

The  present  age,  especially  on  this  continent,  is  one  of  the 
barbaric  use  of  the  mineral  assets  such  as  coal  and  ore.  As  the 
population  increases  and  the  development  of  mines  is  pushed  to 
its  limit,  the  increasing  scarcity  both  of  the  ore  and  of  the  fuel 
to  smelt  it,  will  make  it  necessary  to  spend  more  money  in 
utilizing  these  to  the  very  best  advantage,  using  the  coal  with  the 
greatest  economy  and  extracting  every  possible  product  from  the 
ore.  It  has  been  suggested  that  the  present  enormous  produc- 
tion of  iron  and  steel  for  example  can  only  represent  a  temporary 


FUTURE    DEVELOPMENTS.  IQI 

condition,  that  of  extracting  the  iron  from  its  ore.  When  most 
of  the  iron  ores  have  been  converted  into  iron  or  steel  our  de- 
scendants will  have  to  be  content  to  use*  over  again  the  metal  so 
produced,  merel}7  making  good  the  deficiency  caused  by  rusting 
and  the  increase  in  population.  Iron  is,  however,  a  very  plenti- 
ful metal,  forming  perhaps  4  or  5  per  cent,  of  the  earth's  crust, 
and  the  coal  will  last  for  a  large  number  of  years,  but  the  time 
must  come  when  it  would  be  extravagant  to  use  coal,  mined  at 
great  expense,  for  the  mere  production  of  heat.  As  coal  be- 
comes more  scarce  it  will  be  used  for  its  chemical  properties  of 
reducing  iron  and  other  metals  from  their  ores,  while  the  neces- 
sary heat  would  be  produced  electrically.  At  that  time  Can- 
adians may  have  to  heat  their  houses  electrically,  or  if,  on  ac- 
count of  the  large  population  in  Canada  at  that  time,  such  method 
cf  heating  were  too  expensive,  they  may  have  to  live  under- 
ground during  the  winter. 

In  the  more  immediate  future  there  will  no  doubt  be  a  great 
development  of  electrical  power,  which  may  in  consequence  re- 
place coal  to  some  extent  in  furnace  operations  such  as  the  pro- 
duction of  steel  and  iron  from  certain  ores,  and  in  certain  locali- 
ties ;  on  the  oth~r  hand  the  rapidly  increasing  market  for  electrical 
power  will  tend  to  keep  the  price  from  falling,  relatively  to  the 
price  of  coal,  and  it  is  therefore  unlikely  that  coal  and  coke  will 
be  at  all  largely  replaced  for  smelting  purposes  by  the  electric 
current  for  many  years  to  come. 

When  the  possibilities  of  the  electric  furnace  have  been 
more  fully  ascertained  it  is  likely  that  some  large  water-powers 
that  are  situated  conveniently  with  regard  to  metallic  ores  may 
be  utilized  for  their  reduction,  the  electric  plant  being  available 
for  other  purposes  after  the  exhaustion  of  the  ore  supply.  At 
the  present  time  such  a  large  return  can  be  obtained  from  capital 
in  Canadian  industries  that  only  the  most  easily  developed  water- 
powers  are  considered.  When  the  country  becomes  more 
thickly  settled  and  when  capital  is  more  abundant,  a  smaller  re- 
turn will  be  expected  and  the  interest  charges  on  permanent  de- 
velopments such  as  hydro-electric  plants  will  be  less ;  thus  en- 
abling powers  to  be  utilized  that  would  be  too  costly  under 
present  conditions. 

With  regard  to  the  probable  future  developments  of  the 
electric  furnace  it  will  be  instructive  to  review  shortly  the  progress 
that  has  already  been  made : — 

I.  The  elec.tric  furnace  has  rendered  available  a  range  of 
temperature  from  about  i,8oo°C.  to  about  3,7oo°C.,  which  could 


192  THE     ELECTRIC     FURNACE. 

not  previously  be  reached,   or  in  other  words  it  has  doubled  the 
available  range  of  temperatures  above  the  freezing  point. 

II.  In  the  electric  furnace  substances  can  be  heated  to  any 
temperature   within   this  increased   range   with   the   complete   ex- 
clusion of  air  or  furnace  gases,  while  with  other  furnaces  it  was 
very  difficult   and   sometimes    impossible  to   exclude   the   furnace 
gases  from  the  substance  to  be  heated. 

III.  The  greater  efficiency  of  the  electric  furnace,  over  the 
fuel   furnace,    which   is   particularly  noticeable   at   high   tempera- 
tures, has  enabled  the  electric  current,  although  more  expensive,, 
to  replace  fuel  for  certain  purposes. 

IV.  The  electrolytic  furnace  enables  a  direct  electric  tension 
to  be  applied  to  break  up  compounds  that  cannot  be  dealt  with 
by  the  ordinary  chemical   reactions  at  high  temperatures. 

The  increased  range  of  temperature  that  is  now  available 
has  resulted  in  a  complete  new  chemistry  of  high  temperatures. 
At  these  temperatures  all  metals  are  reduced  from  their  oxides  by 
carbon,  and  many  of  them  unite  with  more  carbon  to  form  car- 
bides, some  of  which  have  valuable  properties.  Other  com- 
pounds such  as  silicides  and  borides  have  also  been  obtained  and 
studied.  No  doubt  in  the  future  many  other  compounds  will 
be  obtained,  from  the  elements  silicon,  carbon,  calcium,  oxygen, 
and  aluminium,  which  form  such  a  large  proportion  of  the  earth's 
crust,  as  the  work  that  has  already  been  done  in  this  direction 
can  only  be  considered  to  have  scratched  lightly  in  the  virgin  soil 
that  has  been  placed  at  our  disposal.  Counting  in  the  other 
elements,  it  will  be  seen  what  an  immense  field  for  discovery  lies 
open  to  those  who  are  working  with  the  electric  furnace.  An- 
other power  furnished  by  the  electric  furnace  is  the  ability  to 
separate  and  purify  substances  by  fractional  distillation  at  these 
high  temperatures.  What  could  formerly  be  done  by  the 
chemist  in  the  separation  of  organic  liquids  by  distillation  in 
glass  vessels  can  now  be  effected  in  the  electric  furnace  in  the 
case  of  such  bodies  as  iron,  lime  and  silica,  not  to  mention  the 
more  fusible  metals  such  as  gold  and  silver.  The  removal  by 
distillation  in  the  electric  furnace  of  the  ash  forming  matters  from 
anthracite,  during  its  conversion  into  graphite,  is  one  commercial 
example  of  a  process  which  will  no  doubt  be  largely  employed 
in  the  future. 

The  high  temperatures  that  can  be  obtained,  together  with 
the  ease  with  which  air  can  be  excluded,  and  the  high  efficiency 
even  at  high  temperatures,  has  made  it  economical  to  smelt 


FUTURE    DEVELOPMENTS.  193 

electrically  such  metals  as  chromium,  manganese,  tungsten, 
titanium,  and  the  element  silicon,  whose  reduction  had  been 
difficult,  expensive,  and  incomplete  in  ordinary  furnaces.  Other 
elements  will,  no  doubt,  be  added  to  this  list,  and  a  large  number 
of  alloys  and  compounds  of  these  will  certainly  be  discovered. 

The  electrolytic  furnace  has  already  enabled  aluminium, 
sodium,  potassium,  magnesium,  calcium,  barium,  strontium,  and 
other  metals  to  be  obtained  from  their  fused  salts,  together  with 
chlorine  and  other  substances.  Although  most  of  the  ordinary 
metals  that  are  amenable  to  this  treatment  must  have  been  ex- 
perimented with  already,  there  are  no  doubt  many  new  processes 
of  this  character  waiting  to  be  discovered,  and  it  seems  likely  that 
a  far  greater  use  can  be  made  of  the  alkali  and  alkaline  earth 
metals  that  have  been  made  available  in  quantity  by  this  means. 

The  very  high  temperature  of  the  electric  furnace  has  en- 
abled it  to  be  used  for  melting  refractory  metals  and  still  more 
refractory  substances  such  as  silica,  lime,  magnesia  and  alumina. 
The  possibility  of  fusing  these  substances  in  quantity  wrill  lead  to 
fresh  uses  of  these  and  other  materials.  The  conversion  of 
amorphous  carbon  into  graphite  is  an  example  of  a  physical 
change  in  an  elementary  substance  at  a  high  temperature,  that 
may  not  soon  be  duplicated,  though  the  problem  of  its  conversion 
into  the  diamond  is  still  unsolved  commercially. 

One  very  important  use  of  the  electric  furnace  is  for  experi- 
mental work  in  the  laboratory.  Here  the  item  of  cost  is  not 
a  matter  of  great  importance  as  the  operations  are  usually  small 
and  occasional.  The  results  of  such  experimental  work  are 
frequently  very  important  and  far-reaching.  For  such  purposes 
the  electric  furnace  will  be  increasingly  employed,  and  standard 
forms  will  be  devised  for  heating  substances,  and  carrying  out  re- 
actions with  the  complete  absence  of  oxygen,  carbon,  or  other  ob- 
jectionable substance.  Vacuum  and  pressure  furnaces  will  also 
be  constructed  and  employed. 

One  probable  development  of  the  electric  furnace  in  the  near 
future  is  made  possible  by  the  intermittent  use  that  is  made  of 
electric  power  for  lighting  and  motor  purposes.  When  electric 
power  is  produced  hydraulically,  large  quantities  could  be  sold 
for  electric  furnace  work  at  moderate  prices  provided  it  were 
only  used  between  certain  hours.  Although  the  smelting  of 
ores  could  hardly  be  carried  on  in  this  intermittent  fashion,  there 
are  many  purposes  for  which  electrical  heat  could  be  applied  in 
this  way.  One  of  these  has  been  suggested  by  Richard 


194  THE  ELECTRIC  FURNACE. 

Moldenke  in  an  article  entitled  "Electric  Smelting  for  the 
Foundry,"*  in  which  he  suggests  that  foundrymen  should  make 
their  own  steel  castings  by  means  of  the  electric  furnace,  prefer- 
ably the  induction  furnace ;  that  even  iron  castings  would  be 
made  better  in  this  way  than  in  the  cupola,  and  that  the  electric 
furnace  would  be  ideal  for  brass  melting.  Such  operations 
could,  of  course,  be  conducted  continuously,  or  as  has  been  sug- 
gested above,  intermittently  so  as  to  obtain  the  power  more 
cheaply. 

In  conclusion  it  should  be  remembered  that  water-powers 
are  not  the  only  available  source  of  electrical  power  for  furnace 
work.  One  other  important  source  of  such  power  is  the  waste 
gas  from  the  iron  blast  furnace.  This  if  used  in  large  gas 
engines  will  frequently  furnish  a  considerable  amount  of  power 
in  excess  of  what  is  needed  for  running  the  plant,  and  this  excess 
could  be  used  for  the  electric  smelting  of  steel  or  similar  purposes. 
Prof.  J.  W.  Richardst  has  stated  that  there  is  as  much  as  1,000,- 
ooo  horse-power  available  from  this  source  in  the  United  States 
alone. 

For  some  electric  furnace  processes  even  coal  burned  in 
steam  boilers  may  be  used  to  generate  power,  but  a  considerable 
saving  can  now  be  effected  by  the  use  of  coal,  which  need  not 
even  be  of  very  good  quality,  in  gas  producers  for  running  large 
gas  engines. 

Other  sources  of  electric  power,  which  may  be  used  in  the 
future,  when  the  price  of  coal  is  getting  higher,  are  the  immense 
movements  of  water  known  as  the  tides.  Attempts  have  also 
been  made  to  harness  the  ocean  waves  whose  great  power  is  at- 
tested by  many'rock  bound  coasts,  and  although  their  irregularity 
renders  them  unsuitable  for  electric  lighting  and  other  uses  of 
electricity  where  constancy  is  an  essential  factor,  it  would  seem 
possible  that  certain  smelting  operations  could  be  conducted  in 
this  way. 

The  strides  of  physical  science  in  recent  years  have  been  so 
enormous  that  there  seems  to  be  no  limit  to  what  may  ultimately 
be  possible,  and  if  in  the  future  we  are  able,  as  suggested  by  Lord 
Kelvin,  to  draw  endless  supplies  of  power  from  the  ether  itself, 
we  can  await  with  quiet  minds  the  exhaustion  of  the  coal  supplies 
of  the  world. 


*Klectro-chemical    and    Metallurgical    Industry,    vol.    v.,    1907,    p.    42. 
•f-Trans.    Am.    Electrochem.    Soc.,    vol.    iii.,    1903,    p.    67. 


INDEX 


Acetylene,  10,  154-155. 

Acheson,  E.  G.,  10,  11,  54,  65,  143,  144,  146,  149,  153. 

furnaces,  n,  12,  24,  26,  64,  65,  72,  76,  79,  145,  M9,  »5o. 

graphite,  148,  149. 

graphite  company,  77,  144,  146,  148. 

(see    also    carborundum,     electrodes,     graphite     and 

siloxicon). 

Achievements  of  electric  furnaces,  191. 
Acker,  caustic  soda  process,  177-179,  181,  183. 
Air-cooling-  of  furnaces,  35,  57,  58,  59,  157-158. 
in  furnaces,  193. 

nitrates  and  nitric  acid  from  air,  173-174. 
Albro,  use  of  silicon  for  heating-,   172. 
Allevard,  electric  steel  furnace  at,   107. 
Alloys,    aluminium,  6,  186. 
copper,  6,  172. 
ferro-,  12,  136-142. 
silicon,  172. 

Alternating  current,  29,  68,  69,  93-103,   109,   167,  173. 
Alumina,  ore  of  aluminium,  6,  7,  52,  186-187. 
refractory  material,  52,  55,  56,  57. 
Aluminium,    40,  52. 

alloys,  6,   186. 
furnaces,  53,   186-188. 
Hall  and  Heroult  processes,  6,  7. 
heat  from,  172,  186. 
production  of,  7,  185-188. 
uses  of,  138. 
Alundum,  173. 

American  Electric  Furnace  Company,  induction  furnaces,  96,  98. 
American   Electrochemical    Society   Transactions,    50,    77,    78,    83,    84, 

106,    148,    172,    181,    187,   194. 
American  fire-brick,  49. 
Ammeter,  15,  16. 
Amorphous  carbon,  53,  76,  77,  78,  79,  80,  142,  143,  147,  148,  149. 

graphite,  142. 

Amperes,  16,  60-66,  67,  72,  79-80,  (see  also  the  individual  furnaces). 
Analyses,  ferro-alloys,  139-140. 

iron  ores,  121,  125,  126,  133. 
pig  iron,  127. 
silicon,  171. 
slag,  134. 

stee1,  45,  47,  132,  134- 
zinc  ores,  165,  170. 
Andreoli,  quotation  from,  3. 
Anode,  174-187. 

Anthracite,  calorific  power  of,  43. 
Araya,  Spain,  induction  steel  furnace  at,  99. 


196  INDEX. 

A. 

Arc,  electric,  i,  2,  3,  19,  21,  32,  53,  61,  67,  173- 

furnaces,   i,  3,  4,  5,  8,    10,   19,  20,  60-62,  66-69,  7',  74,  87-92,   129- 

131,  159,  173- 
furnaces,  direct-heating-,   19-20,  32,   (see  Girod,  Heroult,  Higgins, 

Salgues,  Siemens,  and  Willson. 
furnaces,  independent,   19,  32,  see  Birkeland  and  Eyde,  Moissan, 

Siemens,  and  Stassano. 
Hg-ht,  i,  2. 
resistance  of,  67. 
voltage  of,  60-62,  67-69,  173. 
Arsem,  vacuum  electric  furnace,  83. 
Ashcroft,   sodium  process,  181-183. 
Ashcroft  and  Swinburne,  chlorine  smelting  process,  184-185. 

B 

Baird,   California,  electric  smelting  of  iron  ores,   14,    107,    121. 
Balance  sheet  of  heat,  46. 
Barium,   193. 

Barnes,  Dr.  H.  T.,  specific  heat  of  water,  38. 
Barus,    thermo-electric  pyrometry,  82. 
Battery,  electric,   i,  3. 
Bauxite,  ore  of  aluminium,  52,    186-187. 
refractory  material,   52,   55,  56. 
Beard,  heat  insulation,   56. 
Becket,   F.  M.,  use  of  silicon  for  reducing  metals,    141,   172. 

water-jackets  for  electrodes,  80. 
Bennie,  P.   McN.,  Gin  steel  furnace,    105. 
Bergamo,   Italy,   zinc  in  electric  furnace  at,   170. 
Bertani,  and  Casaretti,  zinc  in  electric  furnace,  170. 
Bessemer  furnace,  86,  91,  92. 

steel,  12,  85,  86. 

Birkeland  and  Eyde,  nitric  acid  in  electric  furnace,  173. 
Bisulphide   of  carbon,    production   in   electric  furnace,    174. 
Bituminous  coal,  calorific  power  of,  43-44. 

use  of  in   electric  furnace,    124. 
Blast  furnace,  coke  used  in,   13,  41,  no. 

efficiency,  41,    123,    128. 

elimination   of   sulphur   and  phosphorus,    132. 
Boiling  temperature  of  carbon,  53,  55. 
Borchers,  Dr.  W.,  9. 

electric  furnaces,  24,  60,   76,  80. 
"Electric  Smelting-  and  Refining,"  3,  4,  5,  6,  24,  155. 
Boudouard,  O.,  temperature  measurements,  50,  52,  53,  56,  82. 
Boys,  C.  V.,  quartz  filaments,  172. 
Brass,  40. 
Bricks,  refractory,  49-58,   (see  also  alumina,  bauxite,  carbon,  dolomite, 

fire-clay,  magnesia,  and  silica. 
Bristol,  W.  H.,  electric  furnace,  22. 

thermo-electric  pyrometer,   83. 
British  thermal  unit,  33,  38-39,  40,  43. 
Bronze,  aluminium,  6. 

in  construction  of  electric  furnaces,   80,   87,    152. 
Brown,  W.  G.,  steel  from  ore  in  electric  furnace,   133. 
Bunsen  battery,  3. 
Burgess,  G.  K.,  pyrometry,  82,  83. 


INDEX.  IQ7 

B 

Burning-  gases  from  electric  furnace,  6,  10,  110,  113,  115,  120,  122-128, 

131,  164. 
heat  from  burning  fuel,  33,  36,  39,  41-44- 


Cables,  electric,  15-18,  67,  80,  81,  105,  106,  108,  117,  119. 
Calcium,   10,  99,   184,  193. 

carbide,  9,   10,   12,  51,  1 54-155- 
hydride,  184. 
nitrate,    173-174. 

California,  electric  smelting  in,  14,  121. 
Callender,  resistance  pyrometer,  82. 
Calorie,  38,  46. 

Calorific  power  of  fuels,  and  electrical  energy,  33,  36,  39,  4!~44- 
Calorimeter,  41,  42. 
Calorite,   substitute  for  thermit,  172. 
Canada,  electric  heat  in,  191. 

electric  smelting  in,  13,  14,  36. 
Canadian  iron  ores,  121. 

Government  Commission,  13,  etc.,   (see  Haanel). 

Capacity  of  electric  furnaces,  45,  88,  90,  91,  92,  95,  96,  99,   100,   106, 
132,  144- 
Carbide  of  calcium,  9,   10,  12,  53,   1 54-155- 

silicon,    (see  carborundum). 
Carbides,  9-12,  136,  149-1 55. 
Carbon,  amorphous,  53,  76,  77,  78,  79,  80,  142,   143,  147,  148,  149. 

blocks,   25,    26,    53. 

boiling  point  of,  53,  55. 

calorific  power  of,  43. 

crucibles,  8. 

diamond,  3,  53,  142. 

electrodes,   i,  2,  4,  5,  °,  17,  23,  48,  53,  77,  78,  79,  80,  Si,   131. 

furnace  linings,  8,    12,   53,  54,   108,    112,   117,   119. 

graphitic,  (see  also  graphite),  53. 

for  reducing  ores,   86,    107-135,    137,   138,   i55-i/o,    iQt- 

in  iron  and  steel,  12,  85,  125,   127,  129,  134. 

National  carbon  company,  77. 

pole  or  point,   i,  2. 

refractory  material,  8,  53,  55,  108. 

resistivity,  53. 

retort    carbon,  6,  54,  79. 

rods,  2,  24,  144,  146,  M9,  152,  153- 

tubes,  23. 

vapour,  2. 

Carbon  bisulphide,   174. 
Carbon  monoxide,  calorific  power  of,  43. 
Carborundum,    10-12,  54-57,   i5oT53- 
discovery  of,  10,  149. 

furnace,  n,  12,  24,  150-153,  (see  Acheson). 
uses,  n,  54,  55,  56,  153- 
fire-sand,  54,  55,  56,  57,   152. 
Carburite,  46. 

Casaretti  and  Bertani,  electric  zinc  smelting,.  170. 

Casing  of  furnaces,  17,  23,  48,  59,  87,  94,  98,   103.,   108,  nx),   113,   115, 
120,   129,  130,  161,   169. 

14 


iy8  INDEX. 

c. 

Casting-  of  metals,  frontispiece,,  96,  194. 

!Cast  iron,   40,  85. 

Castner,   sodium  process  and  furnace,   179-181,   182. 

Castner  Kellner  Company,  chlorine  smelting  process,   185. 

Cathode,  2,  174-187. 

Caustic  soda,  Acker's  process  and  furnace,   177-179. 

electrolysis,  179-183. 

Champagne   (Ariege)   France,  electric  zinc  smelting  at,  161. 
Chappuis,  thermo-electric  pyrometry,  82. 
Charcoal,   calorific  power  of,   43-44. 

for  reduction  of  ores,   109,   no,  m,    115,    120,    124,    125,    126, 

127,    128. 

furnace  lining,   3,  6,   53. 

Charging  and  discharging  furnaces,  17,  (see  also  individual  furnaces). 
Chats  Falls,  cost  of  electric  power  from,  34. 
Chemical  energy,    16,    176. 
Chlorine,  30-31,   177-179,   184-185. 
Chromite,  52,   106. 
Chromium,    12,   136-141. 

Clarke,  Dr.  F.  W.,  Silicon  in  earth's  crust,  171. 
Classification  of  electric  furnaces,    18-32. 
Clay,  (see  fire-clay),  49-50,  54,  55,  57,  58,  98. 
Coal,  calorific  power  of,  33,  43-44. 
supplies  of,  189-191. 
use  of  in  electric  furnace,    124. 
Coal  gas,  calorific  power  of,  43,  44. 
Coke,  calorific  power  of,   43,   44. 

for  cores  of  electric  furnaces,  74,  75,  76. 
for  crucible  steel  furnaces,  34,  36,  39. 
for  iron  blast-furnace,   13,  41,  no. 
for  lining  electric  furnaces,   53. 
for  reduction  of  ores,   124,   128. 
graphitized,  76. 
resistivity  of,  53. 

Colby,  induction   steel   furnace,    13,   30,   96-99,    101. 
Collins,   (or  Collens),  C.  L.,  Uses  of  Acheson  Graphite,  148. 
Conclusions,  83-84. 
Conduction  of  heat,  57,  58. 
Conductivity   of  molten  metals,  72,  78,    101,    105. 

molten   slags,  74,  78. 
Conley,  electric  furnace,  23. 
Construction  of  electric  furnaces,    17,  48-84. 

Consumption  of  electrical  energy  in  electric  furnaces,   46,   47,   48,  49, 
58,   89,  90,  92,  96,  98,    100,    in,    113,    125,   126,    127,   128, 
131,  137,  153,  170. 
of  electrodes,  80,  131. 
Contents    of   electric   furnaces,    solid,     26,    32,      (see     also     individual 

furnaces), 
melting,    26-28,    32,    66,    69,    (see   also 

individual   furnaces), 
liquid,   28-32,    72,    (see   also   individual 

furnaces). 

Continuous  electric  furnaces,  10,  17,  49. 

Cooling  of  electrodes  by  water,  4,  5,  59,  60,  80,  81,  87,  105,  130,  173. 
furnaces,  by  air,  35,  57,   58,  59,   157-158. 

by  water,  29,  57,  58-60,  94,  97,  161. 


INDEX.  1 99 

C. 

Copper,  aluminium  alloys,  6. 

cables,  15-18,  67,  80,  81,  105,  106,  108,  117,  119. 
construction   of   electric   furnaces,    80,  97,  98,    103,    109,    115, 

152,  167. 

melting  temperature  and  heat  required  to  melt,  40. 
silicon  alloys,  172. 
vaporized,  5. 

Cores  of  resistance  furnaces,  18,  24,  25,  26,  74,  75,  144,  146,  149,  150,  151. 

broken  coke,  74,  75,  76,  151,  152. 
carbon  blocks,  25,  26. 
carbon  rods,  24,  144,  146,  149. 
construction  of,  25,   151,  153. 
multiple  cores,   153-154. 
resistance  of,  24,  7-5-78,  144-152. 
retort  carbon,  6. 
Corundum,  artificial,  173. 
Cost  of  fuel  and  electrical  power,  13,  33,  34,  36,  37,  47,  90,  96,   121, 

189,  190,  IQI,  193,  194- 
electrical  smelting-,  73,  92,   128. 
electrodes,  90,  131. 
pig-iron,    121. 
steel,  47,  QO,  135- 

Cowles,  E.  H.  and  A.  H.,  5,  6,  26,  157. 

aluminium  furnace,   10. 

electric  zinc  furnace,    157. 

Crocker,  F.  B.,  "Electric  lighting,"  67. 

Crucible,  8,  54,  94,  96,  97,  98,  142,  143. 

electric  furnace,  3,  4,  5,  22,  (see  Bristol,  Colby,  Evans,  Girod, 

Howe,  McGill,  Napier,  Siemens, 
steel  furnace,  34,  35,  36,  86,  94. 
steel,  85,  86,  88,  89,  91,  97- 
Cryolite,  7,   187. 
Crystalline  graphite,  142. 

Current,   alternating,  29,   68,  69,   87,  93-103,   109,    173. 
continuous  or  direct,  30,   165,  174. 
electric,  2,  3,   15-18,    (and  under  other  headings). 

D. 

Davy,  Sir  Humphry,  i. 

Definition    of    electric  furnace,    15. 

De  Laval  electric  furnaces,  28,  29,  59,  72,  80,  135,  158,   159. 

Demond,  C.  D.,  temperature  measurements,  49,  82. 

Design  of  electric  furnaces,  48-84. 

Despretz,  electric  furnace,  3. 

Development  of  electric  furnaces,  i,  3,  189-194. 

Diamond,  a  form  of  carbon,  3,  53,  142. 

production  of,  in  electric  furnace,  3,  7,  9,   142. 
Direct  current  arc,  2. 
Direct-heating  arc  furnace,    19-20,  32,    (see  Girod,   Heroult,    Higgins, 

Salgues,  Siemens,  Willson. 
Direct  or  continuous  current,  30,   165,    174. 
Direct  production  of  steel  from  the  ore,   129-135. 
Disc  of  flame,    173. 
shaped  furnace,  173. 


200  INDEX. 

D. 

Discovery  of  carborundum,  10,  149. 

electric  arc,  i. 

electric  battery,  i. 

electric   furnace  graphite,    11,    143. 

principle  of  electrical  heating^   3. 

Dissociation  of  silicon  carbides,  55,  56,   143,   147,   149,    152,   153. 
Distillation  of  metals  in  electric  furnace,  5,  8,  147,  192. 

zinc,   157-170. 
Diston,   Henry  and  Sons,  Colby  induction   steel  furnace,   frontispiece, 

97,  99- 
Dolomite,  refractory  material,   52,  87,  94,   113. 

lining"  for  electric  furnace,  87,  88,  94,  112,  113. 
Duesseldorf,  carborundum  plant  at,   153. 
Dupre,  A.,  explosive  gas  from  ferro-silicon,   141. 
Dynamo  electric,  3,   15,    16,    18,    167. 


Edstrom,  J.  S.,  electrical  extraction  of  nitrogen  from  the  air,  173. 
Efficiency  of  furnaces,  33-47,   123-128,   192. 
calculation  of,  37-46. 
used  for  melting  metals,  34,  36. 

Eichhoff,  Prof.,  operation  of  Heroult  steel  furnace,  89, 
Electric  arc,    i,  2,  3,   53. 

arc  furnace,   (see  arc  furnaces), 
battery,   i,  3. 

cables,  15,  16,  17,   18,  So,  Si,   105,  106,  108,  117,   119. 
circuit,   15,  16. 

current,  2,  3,   15-18,  (see  also  other  headings), 
dynamo,  3,  15,  16,  18. 

energy,  amount  used  in  furnaces,  46,  47,  48,  49,  58,  89,  90,  92, 
96,  98,  100,  in,  113,  125,  126,  127,  128,  131,  137, 
153,  170. 

heating  power  of,  15-17,  33,  43,  46,  189-194. 
furnaces,    (see    arc    continuous,    crucible,    electrolytic,    experi- 
mental, ideal,  induction,  intermittent,  pressure,  resistance, 
smelting,  tube,  vacuum). 

see  aluminium,  alundum,  barium,  calcium,  calcium 
carbide,  calcium  nitrate,  caustic  soda,  carbon  bisulphide, 
carborundum,  chlorine,  copper,  diamond,  ferro-alloys, 
fused-quartz,  glass,  graphite,  graphite  electrodes,  iron, 
nitrates  and  nitric  acid,  phosphorus,  platinum,  potassium, 
siloxicon,  sodium,  steel,  strontium,  zinc. 

see  Acheson,  Acker,  Arsem,  Ashcroft,  Birkeland, 
Borchers,  Bristol,  Castner,  Colby,  Conley,  Cowles,  Des- 
pretz,  Evans,  Eyde,  Faure,  Gin,  Girod,  Gronwall,  Haanel, 
Hall,  Harmet,  Harker,  Heroult,  Higgins,  Howe,  Imray, 
Ischewsky,  Jacobs,  Johnson,  Keller,  Kjellin,  Laval,  Lind- 
blad,  McGill,  Moissan,  Napier,  Patterson,  Pepys,  Pichou, 
Potter,  Reynolds,  Ruthenburg,  Salgues,  Siemens,  Snyder, 
Stansfield,  Stassano,  Swinburne,  Tone,  Tucker,  Turnbull, 
Willson. 

see  achievements,  air-cooling,  classification,  construc- 
tion, cores,  costs,  current,  current-density,  definition,  de- 
sign, development,  dimensions,  discovery,  distillation, 


INDEX.  201 

E. 


Electric  furnaces,  continued. 


efficiency,  electrodes,  envelope,  future,  heat,  history,  lin- 
ing's, materials  of  construction,  measurements,  operation, 
output,  production,  regulation,  resistance,  resisting-con- 
tents,  resistors,  tapping,  temperature,  uses,  voltage,  walls, 
water-cooling. 

furnace  company,  American,  induction  furnaces,  96,  98. 
heat,  2,  6,  15,  16,  33,  43,  189-194. 
horse-power-year,  heating  value  of,  33,  43,   190 
inductance,    17,  101,   103. 
inertia,   17. 
light,    i,   2. 

power  used  in  furnaces,  3,  8,  12,  45,  46,  60-66,  68,  69,  70,  72, 
73,  89,  90,  93,  95,  96,  98,  99,   100,  106,   120,    121,   131, 
137,  138,  146,  150,  152,  155,  160,  161,  165,  170,  173,  178, 
181,  183,  190. 
resistance,   15-17. 
resistivity,   76-78. 

transformers,  18,  67,  93,  94,  97    101,  102,  105,   108,   117,   119. 
voltage,   66-71,    (see  also  individual   furnaces). 

Electrical  Metallurgical  Company,  ferro-alloys  in  electric  furnaces,  138. 
Electrochemical  and  Metallurgical  Industry,  frequent  references. 
Electrochemical  Society,  American,  transactions  of,  (see  American). 
Electrodes,  i,  2,  4,  5,  17,  53,  59,  60,  67,  71,  77,  78,  79,  80,  81,  113,  (see 

also  individual  furnaces), 
central,  27,   28. 
copper,  5,  175,  177. 
holders,   n,   17,  80-8 1. 
lateral,  26,  27. 
positive,  4,  5- 

water-cooled,  4,  5,  59,  60,  80,  81,  130,  173. 
Electrolysis,  2,  6,  30-31,  32,    165,    174-17?- 
Electrolytic   furnaces,   7,    15,   30-31,   32,    177-183,    187,    192,    (see   also, 

Acker,  Ashcroft,  Castner,  Hall,  Heroult,  Swinburne. 
Electro-magnet,  173. 
Electrons,    2. 
Electro-quartz,  172. 

Energy  used  in  electric  furnaces,    (see  electric  energy). 
Engelhardt,  V.,  operation  of  induction  furnace,  95,   100. 
England,  steel  in  electric  furnace  in,  36,  99. 
Envelope  refractory  of  electric  furnace,   17,  48. 
Essen,  Germany,  electric  steel  furnaces  at,  99,    106. 
Essential  parts  of  electric  furnace,   17. 
Ethylene,  C2H4,  calorific  power  of,  43. 
European  Commission  Report,    (see  Haanel). 
Europe,  electric  smelting  of  iron  and  steel,  in,   13. 

electric  zinc   smelting  in,    160. 

Evans,  J.  W.,  steel  from  ore  in  electric  furnace,  132-134. 
Evaporative  heat  unit,  38-39. 

Expansion  and  contraction  of  refractory  materials,  50,  51. 
Experimental  electric  furnaces,  21,  22,   23,   163-164,    193. 
Experiments  at  Sault  Ste.   Marie,    (see  Haanel). 
Eyde  and  Birkeland,  nitric  acid  fr.^m  air,  in  electric  furnace,   173. 


202  INDEX 


Faure,  electric  resistance  furnace,,  5. 
Ferro-alloys,    12 ,    136-142. 

chromium,  12,  136-142. 
manganese,  12,  136-141. 
molybdenum,   12,   138,   140,  141. 
nickel,  12. 
silicon,   12,    136-142. 
titanium,    12,   136-141. 
tungsten,   12,   136-141. 
vanadium,   138,   140,   141. 
Ferro-alloy  works,  Girod,  138-139. 

Fery,   optical  measurement  of  temperature  of  arc,   53. 
Fire-clay,  49-50,  54,  55,  57,  585.98,  157. 

FitzGerald,  F.  A.  J.,  electric  furnace  design  and  Acheson  furnaces  and 
furnace  products,   n,  23,  54,  65,  73,  75,  77,  83,  143,   146,   152,   153. 
Forssell  and  FitzGerald,  resistivity  of  carbon,  77. 
France,  electric  furnaces  in,    12,  45,   113,   160. 
"Fuel  and  Refractory  Materials,"  A.  H.  Sexton,  49,  50,   51,   52. 
Fuel,  calorific  power  of,  33,  36,  39,  41,  42,  43,  44. 

oil,   calorific  power  of,  43. 
Furnaces,  Bessemer,  86,  91. 

blast,    13,  85,    107,    no,    in,    112,    121,    128,   129. 
charging  and  discharging,  17,  (see  also  individual  furnaces), 
construction,   17,  48-84. 
continuous,  10,  17,  49 
crucible  furnace,  34,  35,  36. 
design,   48-84. 

electric,    (see  electric  furnaces), 
efficiency,   33-46,    123-128,   192. 
intermittent,  7,   10,  48. 
linings,   (see  linings  of  furnaces), 
operation,  48-84. 

open-hearth,  34-35,  36,  50,  86,  88,  90,  92,   132,   135. 
reverberatory,  34-35,  36. 
shaft,    34-35,    135. 
Fused-quartz,   22,   172. 

magnesia,   52. 
Future   developments   of  electric  furnace,    189-194. 


Gas    carbon,  6. 

coal  gas,  calorific  power  of,  43-44. 

from  electric  furnaces,  6,  10,  35,   no,    113,    115,   120,   122-128,   130, 
131,    156,    157,    164. 

in  furnaces,   5,   167,    173. 

Germany,  electric  steel  furnaces  in,  36,  91,  99,   106,   131. 
Gin,  steel  furnaces,  30,  60,  64,  66,  72,  78,  80,  86,  101,  104,  105,  106,  107. 
Girod,  electric  furnaces  and  ferro-alloys,  106,  107,  138. 
Glass  in  electric  furnace,  172-173. 
Goldschmidt,  Dr.,  Stassano    steel  furnace,  61,  131,  135. 

thermit  process,   141,   172,    186. 
Gram-calorie,  38,  39. 


INDEX.  203 

c. 

Graphite,  142-149. 

Acheson,   n,  12,   143-149. 

amorphous,  142. 

Company,  Acheson,  77,   144,   146,   148. 

crucibles,  97-98,   142,   143. 

crystalline,  142. 

electric,  Q,   u,    12,  143-149- 

electrodes,  53,  144-148 

furnace,  26,   144-149,   (see  Acheson). 

packing-,  115. 

refractory  material,  53,   54,  98,   142,   143- 

soft,  149. 

Gray,  G.   W.,  analysis  of  ferro-alloys,  139. 
Gronwall  furnace,  30,   101. 

Guldsmedshyttan,  Sweden,  induction  steel  furnace  at,  99. 
Gysinge,  Sweden,  induction  steel  furnace  at,  93-96,  99. 


Haanel,  Dr.    E.,    13,    14,   67. 

Report  of  European  Commission,  14,  34,  45,  62,  63, 
64,  69,  70,  71,  78,  81,  86,  88,  89,  92,  93,  95,  105, 

106,  in,   113,   130,   131. 

Report  of  experiments  at  Sault  Ste.  Marie,  69,  81,  101, 

107,  108,  no,  115,  117,  120,  121,  126,  135. 
Haanel-Heroult,  electric  furnace,  28,  115-117. 

Halcomb  Steel  Company,  Syracuse,   Heroult  steel  furnace,  90. 
Hall  aluminium  process  and  furnace,  6,   187. 
Hallstahammar,  electric  zinc  smelting-  at,   160. 
Harbord,  F.  W.,  electric  furnace  steel,  89,  95. 

"The  Metallurgy  of  Steel,"  139. 
Marker,  J.  A.,  electrical  tube  furnace,  23. 

melting  temperatures  of  metals,  40. 
thermo-electric  pyrometry,  82. 

Harmet,  electric  furnace  for  iron  ores,  13,  27,  72,   113-115. 
Heat,  balance  sheets,  46. 
calories,  38,  46. 

cost,    13,  33,  34,  36,  37,  47,  90,  96,    121,   189-194. 
efficiency,  33,  47,  123-128,  192. 

from  burning-  fuel,   (calorific  powers),  33,  36,  39,  41-44. 
from  electric  current,  2,  6,   15,   16,  33,  43,  46,    189-194. 
from  silicon,  172. 
insulation,  56. 
losses  of,  35,  36,  37. 
meaning-  of,  37. 

production  of  in  electric  furnace,  48,  60-66. 
specific  heat  of  water,  38. 
to  melt  metals,  40. 
units,  38,  39. 
ITeroult,  Paul  T.,  aluminium  furnace,  6. 

electric   steel  furnaces,   12,   13,  20,   44-47,    59,   62,  66, 
68,  69,  71,  80,  81,  86-92,  94,  95,  101,  106,  107,  171. 
electric  ore-smelting-  furnaces,   13.   14,  28,  49,  53,  02, 
63,  64,  66,  67,  70,  78,  81,  107,  108-111,   112,   113, 
126,  128,  129,  133,   137,  169. 
Heroult-Haanel,  electric  furnace,  28,   115-117. 


204  INDEX. 

H. 

Heroult-Turnbull,  electric  furnace,  117-121,,   127. 

Hig-g-ins,  A.  C.,  electric  furnace,   173. 

Hofman,  H.   O.,  melting-  temperatures  of  clays,  49,  Seg'er  cones,  82. 

Horse-power  used    in   electric  furnaces,    12,    33,    34,   36,    43,    (see    also 

electric  power  used  in  furnaces. 
Howe,  Prof.  H.  M.,  electrical  crucible  furnace,  22. 

melting-  temperatures  of  cast-iron,  40 
Hunt,  Dr.  T.  Sterry,  Cowles'  electric  furnace,  6. 
Huntingdon  and  Siemens,   electric  furnace,    i,  5. 
Hutton,  Dr.  R.  S.,  cost  of  water-power,  34. 

electrical  tube  furnace,  23. 

ferro-alloys,   138,   140. 

Girod   steel  furnace,    106. 

heat  insulation,  56. 
Hydrogen,  calorific  power  of,  43. 
Hydrolith,  184. 

Ibbotson,  E.  C.,  Kjellin  steel  furnace,  95. 

Ideal  electric  furnace,  48,    122-128. 

Imray,   O.,  electric  furnace  graphite,   144. 

Independent    arc   furnaces,    19,    32,    (see    Birkeland    and    Eyde,    Laval, 

Moissan,  Siemens,  Stassano. 
Inductance,    17,   101,    103. 
Induction  furnaces,   29,  30,   80,  93-105,   166-167,    (see  Colby,   Gronwall, 

Kjellin,  Snyder. 
Inertia  electrical,  17. 
Insulation,  electrical,  120. 

of  heat,   56,    57.    58. 
Intermittent  electric  furnaces,  10,   17,  48,   (see  also  Acheson,  Borchers, 

Colby,  Cowles,  Gin,   Gronwall,  Johnson,   Kjellin,   etc. 
International  Acheson  Graphite  Company,   77,    144,    146,   148. 
International  Calcium  Company,  Switzerland,  induction  steel  furnaces, 

99. 
Iron,   alloys,   12,    136-142. 

blast-furnace,   13,  85,   107,  no,   in,   112,   121,   128,  129. 

casing-  of  electric  furnaces,    59,   87,   94,    103,    108,    109,    113,    115, 

120,  129,  161,  169. 
cast,  40,  85. 

COSt    of,     121. 

pig-,  49,   85,  86,   107-129. 

reduction  from  ore,  49,   86,   107-135. 

smelting-,   electric,   13,    14,   107-129,    (see  Girod,   Haanel,   Harmet, 
Heroult,  Keller,  Turnbull). 

volatilized,   12. 

wrought,    40,   85. 

Ischewsky,   B.  Von,  rotary  electric  furnace,  23. 
Italy,   electric  zinc   smelting,    170. 

Stassano  steel  furnace,   13,   130. 

J. 

Jacobs,  C.  B.,  production  of  alundum  in  electric  furnace,  173. 
Johnson,  W.  McA.,  electric  zinc  furnace,  26,   157-158. 

uses   of  Acheson  grnpbite,    148 
Joule,  3- 
Judd,  E.  K.,  graphite,   142. 


INDEX.  205 

K 

Kaolin,  49. 

Kathode  (or  cathode),  2,  174-187. 

Keller,  electric  smelting-  of  iron,  steel,  and  ferro-alloys,  12,  129,  135,  137. 

electric  steel  furnaces,  92,  107,  135. 

ore-smelting-  furnace,  13,  14,  63,  64,  69,  70,  71,  78,  80,  in,  113. 
Kelvin,   Lord,   energy  from  the  ether,    194. 
Kilogram  calorie,  38-39. 
Kjellin,  induction  steel  furnace,   12,  13,  30,  32,  64,  66,  72,  78,  80,  86, 

93-96,  97,  98,  99,  101,   105,  106,  107. 
Kortfors,  Heroujt  steel  furnace  at,  69,  8<S. 
Krupp  works,  Essen,  electric  steel  furnaces,  99,  106. 
Kryptol,  23,  149. 

L 

Lake  Superior  Power  Company,  in. 

Lampen,  A.,  high  temperature  measurements,  50,   51,  55,  56,  83,   153. 

Lanyon  Zinc  Company,    157. 

La  Praz,  Heroult  steel  furnace,  45,  62,  69,  88. 

Lathe,  F.  E.,  steel  from  ore  in  electric  furnaces,  133. 

Laval  De,  electric  furnaces,  28,   29,   59,  72,  80,    135,    158,   159. 

Lead,  40,  161-170. 

Le  Chatelier,  high  temperature  measurements,  53,  82. 

Le  Leux  Keller  and  Co.,  electric  smelting-,   113. 

Lenher,  V.,   H.    Moissan,    "The  electric  furnace,"   trans,   by,   7. 

Lewes,  F.  B.,  "Acetylene,"  155. 

Light  electric,   i,  2. 

Lime,  refractory  material,  50-51,  55,  56,  57,  60,  61. 

Limestone,  refractory  material,  8,  61. 

Lincoln,  P.  M.,  resistivity  of  carbon,  77. 

Lindblad,  electric  induction  furnace,   101. 

Linings  of  furnaces,  8,  12,  23,  45,  53,  49-60,  96,  112,  113,  132,   (see  also 

individual  furnaces). 

Livet,  France,  Keller  ore-smelting-  furnace  at,  70,  113,  137. 
Lloyd,  M.  B.,  and  Dupre,  explosive  gas  from  ferro-silicon,  141. 
Longmuir,   P.,   analysis  of  ferro-alloys,   139. 
Lotka,  A.  J.,   nitrates  from  air,    173. 
Lucke,   Prof.   C.   E.,   cost  of  water-power,  34. 
Lummer,  temperature  of  arc,  53. 

M 

Mabery,  Prof.  C.   F.,  Cowles'  furnace,  6. 

reduction  of  metals  by  carbon    9. 

Maeulen-Wilson  Company,    articles  of  fused   quartz,    172. 
Magnesia    (magnesite)    refractory  material,   8,    19,    51,    52,    55,    56,   57. 

88,94,  105,  112,  113,   117,   129,  131. 
Magnesium,   184. 
Manganese,   12,  136-141. 
Materials  of  construction  of  furnaces,  49-60,  (see  also  alumina,  b.nuxite, 

carbon,  carborundum,  dolomite,  fire-clay,  lime,  magnesia, 

silica,   siloxicon. 

McGill  University,  electric  crucible  furnace  at,  22. 
Measurements  of  furnace  temperatures,  82,  83. 
Measuring   instruments,    electrical,    18. 
Melted  metals  as  resistors,  29-30,  72,  93-106. 
Melting  contents  of  furnaces,  26  28,  32,  66,  6r>. 


206  INDEX. 

M. 

Melting     metals,   furnaces  for,    22,    (see    Colby,    Gin,    Girod,    Harker, 

Heroult,  Howe,  Kjellin,  McGill,  Moissan,   Siemens). 
Melting  metals,  3,  34,  35,  36,  39,  40,  41,  44-47- 
Melting  temperatures  of  metals,  40,   56. 

refractory  materials,  49-56. 

Metals,  melting  temperatures  and  heat  required  to  melt,  40. 
Metallurgical  calorific  power,  42-43. 
Methane   (marsh  gas),  CH4,  43. 
Miscellaneous   uses    of  electric    furnaces,    171-174. 
Missouri,  fire-clay,  49. 

Moissan  Henri,  electric  arc  furnace,  8,  9,  19,  48,  60,  61,  62,  66,  67,  68, 
69,  80. 

production  of  diamond,  3,   7,  9. 

researches,   7,  9,    56,   155. 

"The  electric   furnace,"   7,    50,   61. 

Moldenke,  R.,  use  of  electric  furnace  in  foundry,  194. 
Molybdenum,    138,    140,    141. 
Mortar  for  fire-bricks,  50,  51. 
Multiple  core  furnace,   153-154. 

N. 

Napier,   electric  arc  furnace,  3. 

National  Carbon  Company,  experiments  on  the  resistivity  of  carbon,  77 

Natural  gas,  43. 

New  Jersey  fire-bricks,  49. 

Niagara  Falls,  cost  of  electric  power  at,  34. 

electric    furnace   operations    at,    12,    54,    138,    146,    173, 

179,  181. 

Nickel,    12,    138,   141. 

Nitrates  and  nitric  acid  from  the  air,  173-174. 
Norton  Company,  manufacture  of  alundum,  173. 
Norway,   cost  of  water-power  in,  34,    174. 

electric  zinc  smelting  in,   160. 

manufacture    of  nitric    acid  from  the    air   in,    174. 
Notodden,  manufacture  of  nitric  acid  from  the  air  at.    174. 


Ohms,  16,  17,  66,  73,  75,  76,  77,  78. 

Oil    (fuel),  43- 

Ontario,  electric  iron-smelting  in,  no,  120. 

Open-hearth  furnace,    2,    34,    35,    36,   46,    86,   87,    88,  90,   92,    132,    135, 

steel,   12,  86,  91,  92. 
Operation  of  electric  furnaces,  48-84,    (and   see  individual  furnaces). 

Heroult  steel  furnace,  89. 
Optical  pyrometry,  82-83. 
Ores,  aluminium,  6,  7,   52,  186-187. 

iron,   13,  14,  45,  85-135,  147,   iQi. 
zinc,   155-170. 
Ore-smelting,   (see  aluminium,  iron,  zinc,  etc.). 

furnaces,  see  Conley,  Cowles,  Evans,  Girod,  Haanel, 
Harmet,  Heroult,  Higgins,  Ischewsky,  Jacobs, 
Johnson,  Keller,  Pichou,  Reynolds,  Snyder,  Stans- 
field,  Stassano,  Tone,  Turnbull,  Willson. 


INDEX.  207 

0 


Origin   of   electric  furnaces,    i. 
Output  of  electric  furnaces,  i,  49. 

aluminium,  7,  188. 

calcium  carbide,    10. 

carborundum,  150,  153. 

ferro-alloys,  137,  138. 

graphite,  143,  H7- 

iron,  no,  120,  121. 

nitric  acid,  174. 

sodium,  181. 

steel,  47,  98,  99,  100. 
Oven,  coke,  43. 


Patterson,  W.  H.,  and  Hutton,  electric  tube  furnace,  23. 
Peat,  fuel,  43- 

Pepys,  W.  H.,  electrical  heating-  of  iron  wire,  3. 
Phosphorus,  in  electrical  furnaces,   174. 

in  iron  and   steel,  88,    132-135. 
Pichou,   electric   arc   furnace,    3. 
Pig  iron,   85,   86,    107-129. 

Pittsburgh  Reduction  Company,  aluminium  furnace,   187. 
Platinum,  melted   in  electric  furnace,    i,    5. 

wire  furnace,   21-23. 

Plattenberg  works,  Westphalia,  Gin  furnace  at,  106. 
Poldihutte    Company,  Austria,  induction  steel  furnace,  99. 
Porcelain,  21. 

Port  -Arthur,  iron  ores  from,  121. 
Potassium,   184,  193. 
Potter,  Dr.  H.  N.,  electric  tube  furnace,  23. 

heat  of  oxidation  of  silicon,   171. 
Pound  calorie,  38,  39,  40,  41,  43. 
Power,  electric,  used  in  electric  furnaces,   (see  electric  power  used  in 

furnaces). 

cost  of,    (see  cost  of  fuel  and  electrical  power). 
Power  factor  of  furnaces,  66,  97,  98,    101-103. 
Pressure  furnaces,    193. 
Price,  E.  F.,  use  of  ferro-silicon,  142. 
Processes,  (see  the  subject  or  the  inventor). 
Producer,  gas,  43. 
Production  of  heat  in  electric  furnaces,  48,  60-66. 

coal,  190. 

Pyne,  F.    R.,   Melting  temperature  of  cryolite,   187. 
Pyrometry,  53,  56,  82,  83. 

Q 

Quartz,  fused,  22,  172. 

Quebec,  Canada,  Charcoal  for  electric  iron  smelting  in,  1 10. 


Reduction  of  metals,  9,   191,   192,   193,  (see  also  aluminium,  iron  and 

zinc. 
I'.egulation  of  electric  furnaces  and  regulating  devices,   18,  71-73,  88, 

89,  109,  113. 


205  INDEX. 

R. 

Refining-  of  steel  in  electric  furnace,  46,  47,  86-94,  132-135. 
Refractory   materials,    17,   49-58. 

alumina,  52,   55,  56,  57. 

bauxite,  52,  55,  56. 

carbon,   8,   53,   55,    108. 

carborundum,    u,    54,    55,  56,    153. 

carborundum-fire-sand,    54,   55,   56,    57,    152. 

dolomite,   52,  87,  94,   113. 

expansion  and   contraction  of,    50,  51. 

fire-clay,  49-50,  54,   55,   57,  98. 

graphite,   53,   54,  98,   142,   143. 

heat  conductivities,   56-58. 

lime,  50-51,  55,  56,  57,  60,  61. 

limestone,  8,  61. 

magnesia,  8,   19,  51,  52,  55,  56,  57,  88,  94,   105, 
112,  113,  117,   129,  131. 

melting   temperatures   of,    49-56. 

porcelain,  21. 

silica,  50,  55,  56,   57,  171,   172. 

siloxicon,  54,  55,  56. 

Remscheid,    Heroult  electric  steel   plant  at,   91. 
Report  of  European  Commission,   (see  Haanel). 

experiments  at  Sault  Ste.  Marie,   (see  Haanel). 
Resistance  electrical,  2,   15,   16. 

furnaces,  3,  16,  21-32,  75-78,   (see  also  individual  furnaces), 
pyrometry,   82. 
Resisting"  contents  of  furnaces,  solid,  26,  32. 

liquid,    28-32,   72,    78. 
melting-,   26-28,  32,  66,  69. 
Resistivity,  electrical,  75. 

amorphous  carbon,  77,  78. 

coke,  76. 

furnace  cores,   24,   75-78,    144-152. 

graphite,  77,  78. 

molten  metals    72,  78,  101,  105. 

slag-s,  74,  78. 

Resistors  of  electric  furnaces,  6,   16,  18,  21-26,  32,  73-78. 
Reverberatory  furnace,  34-35. 
Reynolds,  L.  B.,  electric  zinc  furnace,  164. 
Richards,  Prof.  J.  W.,  39,  78,  92,  144,  147,  150,  153,  180,  194. 

aluminium,   6,    187,    188. 

furnace  efficiencies,  36,  37,   156. 

metallurgical  calculations,  34,  37,  40,  42,  43,  52, 

53,  56,   58,   125. 

Ries,  H.,  New  Jersey,  fire-bricks,  49. 

Roberts-Austen,   Sir  W.    C.,  thermo-electric  pyrometry,   82. 
Rods,  carbon,  2,  24,  144,   146,   149,  152,  153. 
Roechling",  iron  works,  electric  steel  furnaces  at,  99,   ion". 
Rossi  Auguste,  J.,   ferro-titanium,    137,    138. 
Ruthenburg,  electric  furnace,  65,    145. 


Salgues,  electric  zinc  furnace  and  smelting,  28,   if**,,    if,i,    \f,>}   r/'> 
Salt,  electrolysis  of,    170-179,    T<c'i-i83. 
San  Francisco,  price  of  pig-  iron  in,   121. 


INDEX.  20Q 


Sarpsborgr,  Norway,  electric  zinc-smelting"  at,  160. 

Sault  Ste.  Marie,  electric  iron-smelting-  at,  49,  62,  69,  81,  108,  in,  113, 

117,  121,  126,  133. 

Scott,  E.  K.,  refractory  materials,  52,  54. 
Seger  cones,  pyrometer,  82. 

Sexton,  A.  H.,  refractory  materials,  49,  50,  51,  52. 
Shaft  furnaces,    34-35,    (see    also    Conley,    Haanel,    Harmet,    Heroult, 

Keller,  Stansfield,  Tone,  Turnbull. 
Sheffield,  induction  steel  furnaces  in,  99. 
Siemens,  Sir  W.,  electric  arc  furnace,  i,  3,  4,  5,  7,  18,  19,  20,  60,  137. 

open-hearth,  steel,  86. 

Silica   (refractory  material),   50,   55-56,  57,    171,    172. 
Silicon,    12,   136-142,    150,    171-172. 
Siloxicon,  furnace  and  manufacture,  12,  153-154,   (see  Acheson). 

uses  of,  54,  55,  5°- 
Silver  from  clay,   186. 

Smelting:  and  refining,  electric,  (see  Borchers). 
Smelting,  electric,  cost,  73,  92,  128. 
iron  and  steel,   12. 

iron  ores,   13,   14,   107-129,   (see  iron), 
regulation  of,  18,  71-73,   109,   113. 

Smelting   furnace,  electric,   for   ores,    Conley,    Evans,    Girod,    Haanel, 
Harmet,    Heroult,   Higgins,    Ischewsky,    Jacobs,    Johnson, 
Keller,    Pichou,    Reynolds,    Snyder,    Stansfield,    Stassano, 
Tone,  Turnbull,  Willson. 
Snyder,  induction  smelting  furnace,  29,  135,  166,  167. 

electric  zinc  smelting,  165,  167,  168,  170. 
Soda  (caustic),  Acker  process,  177-179. 
Sodium,   Ashcroft   process,    181-183. 

Castner  process,  179-181. 

Sodium  chloride,  electrolysis  of,   177-179,   181-183. 
Source  of  electric  current,  18. 
Spain,  induction  steel  furnace  in,  99. 
Spiegel,   139- 

Stalhane,  O.,  induction  steel  furnace,  101. 
Stansfield,   Dr.   A.,  electric  crucible  furnace,  22. 
electric  zinc  furnace,  164. 

electro-thermic  production  of  iron  and  steel,  36,  133. 
Ideal  electric  furnace,   121-128. 
melting  temperature  of  silica,  50. 
thermo-electric  pyrometry,  82. 
Stassano,  Capt.,  electric  steel  furnace,   13,   19,  48,  61,  62,  66,  68,  69, 

107,  129-131,  133,  135. 
Steel,  85. 

Bessemer,    11,    12,   85,  86. 
cost  of,  90,  135. 
crucible,  36,  85,  86,  88,  89,  91- 
melted  in  electric  furnace,  i,  5,  86-107. 
open-hearth,   12,   86,  91. 

production  direct  from  ore  in  electric  furnace,   129-135. 
production  of,  in  electric  furnace,   3,    12,    13,  44-47,  86-107,    129- 
135,     (see    also    Colby,    Evans,     Gin,     Girod,     Grnnwall, 
Heroult,  Keller,  Kjellin,  Pepys,  Stassano. 
structural,  90,   100,  107,  131. 
tool,  40,  47,  89,  91,  107. 


210  INDEX. 


Steinhart,  O.  J.,  ferro-alloys,  138. 

Strontium,    10,3. 

Sulphur  in  blast-furnace  pig-iron,  132. 

electric-furnace  pig-iron,   no,   in,   128,   132. 

electric-furnace   steel,    88,  99,    132,   135. 
Sweden,  electric  zinc-smelting  in,   160. 

electric   steel-making,    12,   36,  93,  94,    101. 
Syracuse,  Heroult  steel-furnace  in,  90. 


Temperature,  aluminium  furnace,  7. 

definition,  37,  38. 

high  of  electric  furnaces,  2,  3,  7,   15,  24,  33,  55,  143,  144, 
147,   150,    152,    153,    155,    156,    171,    186,    191. 

measurements  of,  82-83. 

of  arc,  2,   53,  56. 

of  electric  furnaces,   12,  48,  49,  56,  77,  82-83,    187,   191- 
193,   (see  also  temperatures,  high,  etc.). 

of  melting  metals,  40. 

of  melting  platinum,  2,  21,  50. 

of  melting  quartz,  2,  50,  55,  56. 

of  melting  refractory  materials,  49-56. 
Thermit,  141,  172,  186. 
Thermo-electric   pyrometry,   82-83. 
Thompson,  S.  P.,  "Electricity  and  Magnetism,"  i. 
Thomson,  3. 

Thomson,   electric  welding,   26. 
Tides,  electric  power  from,  194. 

Tilting  furnaces,  87-88,  96-98,    (see  also  Colby,   Heroult,  Wellman) 
Tin,  40. 

Titanium,   12,   132,    136-141. 
Tone,   F.   J.,  electric  furnaces,  25,    171. 
Tool-steel,  40,  47,  89,  91,  107. 
Transformer,   electric,   18,  67,  93,  94,  97,    101,    102,   103,   105,    108,   117, 

119. 

Trollhattan,  electric  zinc-smelting  at,  160. 
Tube-furnaces,  3,   21-23,    (see  also  Despretz,   Harker,  Hutton,  Potter, 

Tucker). 
Tucker,  S.  A.,  electric  tube  furnace,  23. 

high  temperature  measurements,  55,  56,  83,  153. 
Tungsten,  136-141. 
Turin,  Stassano  furnace  at,  140. 
Turnbull-Heroult,   electric  ore-smelting  furnace,    117-121. 


United  States,  output  of  aluminium  in,  7. 

production  of  electric  steel  in,  36,  97, 
production  of  graphite  in,  143. 

Uses  of  electric  furnace,  86,  136-188,  191-194. 


Vacuum  electric  furnace,  83,  193. 

Vanadium,  138,   140,   141. 

Vancouver,  electric  zinc  smelting  at,  170. 


INDEX.  2  I  I 

V 

Vapour  of  carbon,  2. 

Vaporized  substances,  in  electric  furnace,  2,  5,  8,  12,  147,  157-170,  192. 

Vickers,  Sons'  and  Maxim,  electric  steel  furnace,  99. 

Violle,  temperature  of  electric  arc,  53. 

Volta,  discovery  of  electric  battery,  i. 

Voltage,  of  arc,  67. 

arc  furnaces,  67-69. 

electric  furnaces,  66-71,    (see  also  individual  furnaces). 

electric  supply,  18. 

resistance  furnaces,  69-71,   (see  also  individual  furnaces). 

smelting-  furnaces,  69-71,  (see  also  individual  furnaces). 
Voltmeter,  16. 
Volts,    1 6. 


W 

Waidner,  C.  L.,  methods  of  pyrometry,  82,  83. 

Waldo,  Dr.     Leonard,  production  of  electric  furnace  steel,  96. 

Walls  of  electric  furnace,  21,   (see  also  individual  furnaces). 

Wanner,  optical  pyrometer,  83. 

Water-cooling,  electrodes,  4,  5,  59,  60,  80,  81,  87,  105,  130,  173. 

furnaces,  29,   57,   58-60,  94,  97,    161,   167. 
Water-gas,  43- 

Water-powers,  14,  189,  190,  191. 
Watts,  48,  60-66,  73,    (see  individual  furnaces). 
Waves,  electric  power  from,  194. 

Webber,  R.  F.,  melting  temperatures  of  fire-clays,  49. 
Weckbecker,  J.,  electric-furnace  graphite  from  charcoal,  144. 
Welland,  Ontario,  electric  iron-smelting  at,    14,   107,   120. 
Wellman,  tilting  open-hearth  furnace,  69,  86,  90. 
Westphalia,  Gin  steel  furnace  in,  106. 
Wheeler,  H.  A.,  melting  temperatures  of  fire-clays,  49. 
White-coal,  189. 

Wilbur    mine,    electric    smelting   of  ore   from,    126. 
Willson  Aluminium  Company,  production  of  ferro-chromium,   138. 
Willson,  T.  L.,  calcium  carbide  furnace,  9-10,  20,  53,  59,   155. 
Wilson-Maeulen  Company,  articles  of  electro-quartz,  172. 
Wood,  (fuel),  43. 
Wright,  J.,  "Electric  furnaces  and  their  industrial  applications,"   15, 

25,   53,  173,   174- 
Wrought-iron,  40,  85. 


Zinc,  40. 

electric  furnaces,   30-31,    155-170,    (see   Cowles,  Johnson,   Laval, 

Reynolds,  Salgues,  Stansfield,  Snyder. 
electro-thermic  production  of,    155-170. 
Extraction  Company,  American,   165. 


RETURN  TO  the  circulation  desk  of  any 
University  of  California  Library 

or  to  the 

NORTHERN  REGIONAL  LIBRARY  FACILITY 
Bldg.  400,  Richmond  Field  Station 
University  of  California 
Richmond,  CA  94804-4698 

ALL  BOOKS  MAY  BE  RECALLED  AFTER  7  DAYS 

•  2-month  loans  may  be  renewed  by  calling 
(510)642-6753 

•  1-year  loans  may  be  recharged  by  bringing 
books  to  NRLF 

•  Renewals  and  recharges  may  be  made 
4  days  prior  to  due  date 

DUE  AS  STAMPED  BELOW 
NOV192003 


DD20   15M  4-02 


YC   19533 


4W>/ 
Sg 


THE  UNIVERSITY  OF  CALIFORNIA  LIBRARY 


